0.0.1

.cargo/config.toml

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+[target.x86_64-pc-windows-gnu]
+linker = "x86_64-w64-mingw32-gcc"

.gitignore

@@ -0,0 +1 @@
+/target

Cargo.toml

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+[package]
+name = "rcalc"
+version = "0.1.0"
+edition = "2021"
+build = "build.rs"
+
+[dependencies]
+slint = "1.11"
+
+[build-dependencies]
+slint-build = "1.11"

README.md

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+# rcalc
+
+Desktop calculator for Linux/Windows/macOS, inspired by the Windows Calculator (standard mode).
+
+Built with Rust + [Slint](https://slint.dev).
+
+## Run
+
+```bash
+cargo run --release
+# or
+./dist/rcalc
+```
+
+### Icon (Linux / Wayland)
+
+On **Wayland** the window `icon` property is ignored — the desktop uses
+`.desktop` + `app_id`. Install once:
+
+```bash
+./scripts/install-desktop.sh
+```
+
+Then start **rcalc** from the app menu (or `~/.local/bin/rcalc`), not by
+clicking a random binary path, so KDE/GNOME can match `app_id=rcalc` to
+`rcalc.desktop` and show the icon.
+
+## Features
+
+- Modes: **Standard**, **Programmer**, **Convert**
+- Standard: `+ − × ÷`, `%`, `±`, `1/x`, `x²`, `√x`, memory
+- Programmer: simultaneous **HEX / DEC / OCT / BIN**, sizes **QWORD / DWORD / DINT / WORD / INT / BYTE**,
+  bitwise ops, clickable bits
+  (WORD/DWORD — unsigned DEC; INT/DINT — signed)
+- Convert: **float32 ↔ two 16-bit words** with endian **AB CD / CD AB / BA DC / DC BA**
+- Convert → **Ratio**: float → minimal **num/den** for electronic gear (Byte≤255 / Word≤65535)
+- Convert → **ASCII**: Char ↔ Hex ↔ Dec (control names for NUL…DEL)
+- **CRC**: Modbus RTU CRC-16 + Modbus ASCII LRC from hex bytes (`01 03 00 00 00 0A`)
+- Keyboard input
+
+## Project layout
+
+- `src/engine.rs` — standard calculator logic
+- `src/programmer.rs` — programmer mode logic
+- `src/convert.rs` — float32 / word endian convert
+- `src/main.rs` — UI wiring
+- `ui/app.slint` — Slint interface
+- `dist/rcalc` — release binary

assets/rcalc.desktop

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+[Desktop Entry]
+Type=Application
+Name=rcalc
+GenericName=Calculator
+Comment=Calculator with Programmer, Convert, CRC tools
+Exec=/home/alex/cloud/rust/rcalc/dist/rcalc
+Icon=rcalc
+Path=/home/alex/cloud/rust/rcalc
+Terminal=false
+Categories=Utility;Calculator;Science;Engineering;
+StartupNotify=true
+# Wayland app_id / X11 WM_CLASS — must match set_xdg_app_id("rcalc")
+StartupWMClass=rcalc

build.rs

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+fn main() {
+    slint_build::compile("ui/app.slint").expect("Slint build failed");
+}

scripts/install-desktop.sh

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+#!/usr/bin/env bash
+# Install rcalc launcher + icon for Wayland/XDG desktops (KDE, GNOME, …).
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/.." && pwd)"
+BIN="${ROOT}/dist/rcalc"
+ICON_SRC="${ROOT}/assets/icon-256.png"
+DESKTOP_SRC="${ROOT}/assets/rcalc.desktop"
+
+if [[ ! -x "$BIN" ]]; then
+  echo "Building release binary…"
+  (cd "$ROOT" && cargo build --release)
+  # Prefer project dist/, else cargo target
+  if [[ -x "$ROOT/dist/rcalc" ]]; then
+    BIN="$ROOT/dist/rcalc"
+  else
+    BIN="$(find "$ROOT" /tmp/cursor-sandbox-cache -path '*/release/rcalc' -type f 2>/dev/null | head -1 || true)"
+  fi
+fi
+
+if [[ ! -x "$BIN" ]]; then
+  echo "error: binary not found; run: cargo build --release && cp target/release/rcalc dist/" >&2
+  exit 1
+fi
+
+APP_DIR="${HOME}/.local/share/applications"
+ICON_DIR="${HOME}/.local/share/icons/hicolor/256x256/apps"
+mkdir -p "$APP_DIR" "$ICON_DIR" "${HOME}/.local/bin"
+
+cp -f "$ICON_SRC" "${ICON_DIR}/rcalc.png"
+ln -sfn "$BIN" "${HOME}/.local/bin/rcalc"
+
+# Rewrite Exec to absolute binary path
+sed "s|^Exec=.*|Exec=${BIN}|" "$DESKTOP_SRC" \
+  | sed "s|^Path=.*|Path=${ROOT}|" \
+  > "${APP_DIR}/rcalc.desktop"
+chmod 644 "${APP_DIR}/rcalc.desktop"
+
+# Refresh caches (ignore failures on minimal setups)
+update-desktop-database "$APP_DIR" 2>/dev/null || true
+gtk-update-icon-cache -f -t "${HOME}/.local/share/icons/hicolor" 2>/dev/null || true
+
+echo "Installed:"
+echo "  launcher: ${APP_DIR}/rcalc.desktop"
+echo "  icon:     ${ICON_DIR}/rcalc.png"
+echo "  symlink:  ${HOME}/.local/bin/rcalc"
+echo
+echo "On Wayland: quit rcalc if running, then start it from the app menu"
+echo "(or: rcalc). The dock should show the custom icon."

src/convert.rs

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+//! Float32 ↔ two 16-bit words with Modbus-style endian (AB CD).
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Endian {
+    /// Big-endian: bytes A B C D as-is (Motorola / network order).
+    AbCd,
+    /// Word-swapped: C D A B.
+    CdAb,
+    /// Bytes swapped inside each word: B A D C.
+    BaDc,
+    /// Little-endian: D C B A (Intel).
+    DcBa,
+}
+
+impl Endian {
+    pub fn label(self) -> &'static str {
+        match self {
+            Endian::AbCd => "AB CD",
+            Endian::CdAb => "CD AB",
+            Endian::BaDc => "BA DC",
+            Endian::DcBa => "DC BA",
+        }
+    }
+
+    pub fn all() -> [Endian; 4] {
+        [Endian::AbCd, Endian::CdAb, Endian::BaDc, Endian::DcBa]
+    }
+
+    fn index(self) -> i32 {
+        match self {
+            Endian::AbCd => 0,
+            Endian::CdAb => 1,
+            Endian::BaDc => 2,
+            Endian::DcBa => 3,
+        }
+    }
+
+    pub fn from_index(i: i32) -> Self {
+        match i {
+            1 => Endian::CdAb,
+            2 => Endian::BaDc,
+            3 => Endian::DcBa,
+            _ => Endian::AbCd,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ConvField {
+    Float,
+    Word0,
+    Word1,
+    AsciiChar,
+    AsciiHex,
+    AsciiDec,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ConvPanel {
+    Words,
+    Ratio,
+    Ascii,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum RatioWidth {
+    Byte,
+    Word,
+}
+
+impl RatioWidth {
+    pub fn label(self) -> &'static str {
+        match self {
+            RatioWidth::Byte => "Byte",
+            RatioWidth::Word => "Word",
+        }
+    }
+
+    pub fn max(self) -> u32 {
+        match self {
+            RatioWidth::Byte => 255,
+            RatioWidth::Word => 65535,
+        }
+    }
+}
+
+/// Relative-error precision presets for gear-ratio approximation.
+pub const PRECISION_PRESETS: &[f64] = &[
+    1e-3, 1e-4, 1e-5, 1e-6, 1e-7, 1e-8, 1e-9,
+];
+
+#[derive(Debug, Clone, Copy)]
+pub struct RatioResult {
+    pub num: u32,
+    pub den: u32,
+    pub approx: f64,
+    pub rel_error: f64,
+    pub exact: bool,
+}
+
+#[derive(Debug, Clone)]
+pub struct Converter {
+    endian: Endian,
+    float_bits: u32,
+    /// Text currently being edited in the active field.
+    draft: String,
+    active: ConvField,
+    error: Option<&'static str>,
+    panel: ConvPanel,
+    ratio_width: RatioWidth,
+    precision_idx: usize,
+    /// Current ASCII / Latin-1 code (0..=255).
+    ascii_code: u8,
+}
+
+impl Default for Converter {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Converter {
+    pub fn new() -> Self {
+        Self {
+            endian: Endian::AbCd,
+            float_bits: 1.0f32.to_bits(),
+            draft: "1".into(),
+            active: ConvField::Float,
+            error: None,
+            panel: ConvPanel::Words,
+            ratio_width: RatioWidth::Word,
+            precision_idx: 3, // 1e-6
+            ascii_code: b'A',
+        }
+    }
+
+    pub fn panel(&self) -> ConvPanel {
+        self.panel
+    }
+
+    pub fn set_panel(&mut self, panel: ConvPanel) {
+        self.commit_draft();
+        self.panel = panel;
+        self.active = match panel {
+            ConvPanel::Words => ConvField::Float,
+            ConvPanel::Ratio => ConvField::Float,
+            ConvPanel::Ascii => ConvField::AsciiChar,
+        };
+        self.sync_draft();
+    }
+
+    pub fn ratio_width(&self) -> RatioWidth {
+        self.ratio_width
+    }
+
+    pub fn set_ratio_width(&mut self, width: RatioWidth) {
+        self.ratio_width = width;
+    }
+
+    pub fn cycle_ratio_width(&mut self) {
+        self.ratio_width = match self.ratio_width {
+            RatioWidth::Byte => RatioWidth::Word,
+            RatioWidth::Word => RatioWidth::Byte,
+        };
+    }
+
+    pub fn precision_idx(&self) -> usize {
+        self.precision_idx
+    }
+
+    pub fn precision(&self) -> f64 {
+        PRECISION_PRESETS[self.precision_idx.min(PRECISION_PRESETS.len() - 1)]
+    }
+
+    pub fn precision_text(&self) -> String {
+        let p = self.precision();
+        format!("{p:.0e}")
+    }
+
+    pub fn cycle_precision(&mut self) {
+        self.precision_idx = (self.precision_idx + 1) % PRECISION_PRESETS.len();
+    }
+
+    pub fn ratio(&self) -> Option<RatioResult> {
+        let x = self.float_value() as f64;
+        approximate_ratio(x, self.ratio_width.max(), self.precision())
+    }
+
+    pub fn ratio_num_text(&self) -> String {
+        match self.ratio() {
+            Some(r) => format!("{}", r.num),
+            None => "—".into(),
+        }
+    }
+
+    pub fn ratio_den_text(&self) -> String {
+        match self.ratio() {
+            Some(r) => format!("{}", r.den),
+            None => "—".into(),
+        }
+    }
+
+    pub fn ratio_frac_text(&self) -> String {
+        match self.ratio() {
+            Some(r) => format!("{} / {}", r.num, r.den),
+            None => "—".into(),
+        }
+    }
+
+    pub fn ratio_approx_text(&self) -> String {
+        match self.ratio() {
+            Some(r) => format!("{:.10}", r.approx).trim_end_matches('0').trim_end_matches('.').to_string(),
+            None => "—".into(),
+        }
+    }
+
+    pub fn ratio_error_text(&self) -> String {
+        match self.ratio() {
+            Some(r) if r.exact => "exact".into(),
+            Some(r) => format!("{:.3e}", r.rel_error),
+            None => "—".into(),
+        }
+    }
+
+    pub fn endian(&self) -> Endian {
+        self.endian
+    }
+
+    pub fn endian_index(&self) -> i32 {
+        self.endian.index()
+    }
+
+    pub fn active(&self) -> ConvField {
+        self.active
+    }
+
+    pub fn error(&self) -> Option<&'static str> {
+        self.error
+    }
+
+    pub fn set_endian(&mut self, endian: Endian) {
+        self.commit_draft();
+        self.endian = endian;
+        self.sync_draft();
+    }
+
+    pub fn set_active(&mut self, field: ConvField) {
+        let ok = match self.panel {
+            ConvPanel::Words => matches!(
+                field,
+                ConvField::Float | ConvField::Word0 | ConvField::Word1
+            ),
+            ConvPanel::Ratio => field == ConvField::Float,
+            ConvPanel::Ascii => matches!(
+                field,
+                ConvField::AsciiChar | ConvField::AsciiHex | ConvField::AsciiDec
+            ),
+        };
+        if !ok || field == self.active {
+            return;
+        }
+        self.commit_draft();
+        self.active = field;
+        self.sync_draft();
+    }
+
+    pub fn ascii_code(&self) -> u8 {
+        self.ascii_code
+    }
+
+    pub fn ascii_char_text(&self) -> String {
+        if self.active == ConvField::AsciiChar {
+            return self.draft.clone();
+        }
+        format_ascii_glyph(self.ascii_code)
+    }
+
+    pub fn ascii_hex_text(&self) -> String {
+        if self.active == ConvField::AsciiHex {
+            return self.draft.clone();
+        }
+        format!("{:02X}", self.ascii_code)
+    }
+
+    pub fn ascii_dec_text(&self) -> String {
+        if self.active == ConvField::AsciiDec {
+            return self.draft.clone();
+        }
+        format!("{}", self.ascii_code)
+    }
+
+    pub fn ascii_name_text(&self) -> String {
+        ascii_control_name(self.ascii_code)
+            .map(|n| n.to_string())
+            .unwrap_or_else(|| {
+                if self.ascii_code.is_ascii_graphic() || self.ascii_code == b' ' {
+                    format!("'{}'", self.ascii_code as char)
+                } else {
+                    format!("0x{:02X}", self.ascii_code)
+                }
+            })
+    }
+
+    pub fn float_value(&self) -> f32 {
+        f32::from_bits(self.float_bits)
+    }
+
+    pub fn words(&self) -> (u16, u16) {
+        float_to_words(self.float_value(), self.endian)
+    }
+
+    pub fn float_text(&self) -> String {
+        if self.active == ConvField::Float {
+            return self.draft.clone();
+        }
+        format_float(self.float_value())
+    }
+
+    pub fn word0_text(&self) -> String {
+        if self.active == ConvField::Word0 {
+            return self.draft.clone();
+        }
+        format!("{:04X}", self.words().0)
+    }
+
+    pub fn word1_text(&self) -> String {
+        if self.active == ConvField::Word1 {
+            return self.draft.clone();
+        }
+        format!("{:04X}", self.words().1)
+    }
+
+    pub fn wire_bytes_text(&self) -> String {
+        let (w0, w1) = self.words();
+        let a = w0.to_be_bytes();
+        let b = w1.to_be_bytes();
+        format!("{:02X} {:02X} {:02X} {:02X}", a[0], a[1], b[0], b[1])
+    }
+
+    pub fn ieee_hex_text(&self) -> String {
+        format!("0x{:08X}", self.float_bits)
+    }
+
+    pub fn clear_active(&mut self) {
+        self.error = None;
+        self.draft = match self.active {
+            ConvField::Float => "0".into(),
+            ConvField::Word0 | ConvField::Word1 => "0".into(),
+            ConvField::AsciiChar => " ".into(),
+            ConvField::AsciiHex => "00".into(),
+            ConvField::AsciiDec => "0".into(),
+        };
+        let _ = self.apply_draft();
+    }
+
+    pub fn backspace(&mut self) {
+        self.error = None;
+        if self.active == ConvField::AsciiChar {
+            self.draft = " ".into();
+            self.ascii_code = b' ';
+            return;
+        }
+        self.draft.pop();
+        if self.draft.is_empty() {
+            self.draft = match self.active {
+                ConvField::AsciiHex => "0".into(),
+                _ => "0".into(),
+            };
+        }
+        let _ = self.apply_draft();
+    }
+
+    pub fn input_char(&mut self, ch: char) {
+        self.error = None;
+        match self.active {
+            ConvField::Float => {
+                let ch = ch.to_ascii_uppercase();
+                if !matches!(ch, '0'..='9' | '.' | '-' | '+' | 'E') {
+                    return;
+                }
+                if self.draft == "0" && ch != '.' && ch != 'E' {
+                    self.draft = ch.to_string();
+                } else if self.draft == "-0" && ch != '.' && ch != 'E' {
+                    self.draft = format!("-{ch}");
+                } else {
+                    self.draft.push(ch);
+                }
+            }
+            ConvField::Word0 | ConvField::Word1 => {
+                let ch = ch.to_ascii_uppercase();
+                if !ch.is_ascii_hexdigit() {
+                    return;
+                }
+                if self.draft == "0" {
+                    self.draft = ch.to_string();
+                } else if self.draft.len() < 4 {
+                    self.draft.push(ch);
+                } else {
+                    return;
+                }
+            }
+            ConvField::AsciiChar => {
+                if (ch as u32) > 255 {
+                    return;
+                }
+                self.ascii_code = ch as u8;
+                self.draft = format_ascii_glyph(self.ascii_code);
+                return;
+            }
+            ConvField::AsciiHex => {
+                let ch = ch.to_ascii_uppercase();
+                if !ch.is_ascii_hexdigit() {
+                    return;
+                }
+                if self.draft == "0" {
+                    self.draft = ch.to_string();
+                } else if self.draft.len() < 2 {
+                    self.draft.push(ch);
+                } else {
+                    self.draft = ch.to_string();
+                }
+            }
+            ConvField::AsciiDec => {
+                if !ch.is_ascii_digit() {
+                    return;
+                }
+                if self.draft == "0" {
+                    self.draft = ch.to_string();
+                } else if self.draft.len() < 3 {
+                    self.draft.push(ch);
+                } else {
+                    self.draft = ch.to_string();
+                }
+            }
+        }
+        let _ = self.apply_draft();
+    }
+
+    pub fn negate_float(&mut self) {
+        if self.panel != ConvPanel::Words && self.panel != ConvPanel::Ratio {
+            return;
+        }
+        if self.active != ConvField::Float {
+            self.set_active(ConvField::Float);
+        }
+        if let Some(rest) = self.draft.strip_prefix('-') {
+            self.draft = rest.to_string();
+            if self.draft.is_empty() {
+                self.draft = "0".into();
+            }
+        } else if self.draft != "0" {
+            self.draft = format!("-{}", self.draft);
+        }
+        let _ = self.apply_draft();
+    }
+
+    fn commit_draft(&mut self) {
+        let _ = self.apply_draft();
+        self.sync_draft();
+    }
+
+    fn sync_draft(&mut self) {
+        self.draft = match self.active {
+            ConvField::Float => format_float(self.float_value()),
+            ConvField::Word0 => format!("{:04X}", self.words().0),
+            ConvField::Word1 => format!("{:04X}", self.words().1),
+            ConvField::AsciiChar => format_ascii_glyph(self.ascii_code),
+            ConvField::AsciiHex => format!("{:02X}", self.ascii_code),
+            ConvField::AsciiDec => format!("{}", self.ascii_code),
+        };
+        self.error = None;
+    }
+
+    fn apply_draft(&mut self) -> Result<(), ()> {
+        match self.active {
+            ConvField::Float => {
+                let t = self.draft.trim();
+                if t.is_empty() || t == "-" || t == "." || t == "-." {
+                    return Ok(());
+                }
+                match t.parse::<f32>() {
+                    Ok(v) => {
+                        self.float_bits = v.to_bits();
+                        self.error = None;
+                        Ok(())
+                    }
+                    Err(_) => {
+                        self.error = Some("Invalid float");
+                        Err(())
+                    }
+                }
+            }
+            ConvField::Word0 => {
+                let w0 = parse_word(&self.draft)?;
+                let w1 = self.words().1;
+                self.float_bits = words_to_float(w0, w1, self.endian).to_bits();
+                self.error = None;
+                Ok(())
+            }
+            ConvField::Word1 => {
+                let w0 = self.words().0;
+                let w1 = parse_word(&self.draft)?;
+                self.float_bits = words_to_float(w0, w1, self.endian).to_bits();
+                self.error = None;
+                Ok(())
+            }
+            ConvField::AsciiChar => {
+                let t = self.draft.trim();
+                if t.is_empty() {
+                    self.ascii_code = b' ';
+                } else if let Some(c) = t.chars().next() {
+                    if (c as u32) <= 255 {
+                        self.ascii_code = c as u8;
+                    } else {
+                        self.error = Some("Not Latin-1");
+                        return Err(());
+                    }
+                }
+                self.error = None;
+                Ok(())
+            }
+            ConvField::AsciiHex => {
+                let cleaned: String = self
+                    .draft
+                    .chars()
+                    .filter(|c| c.is_ascii_hexdigit())
+                    .collect();
+                if cleaned.is_empty() {
+                    return Ok(());
+                }
+                match u8::from_str_radix(&cleaned, 16) {
+                    Ok(v) => {
+                        self.ascii_code = v;
+                        self.error = None;
+                        Ok(())
+                    }
+                    Err(_) => {
+                        self.error = Some("Invalid hex");
+                        Err(())
+                    }
+                }
+            }
+            ConvField::AsciiDec => {
+                let t = self.draft.trim();
+                if t.is_empty() {
+                    return Ok(());
+                }
+                match t.parse::<u16>() {
+                    Ok(v) if v <= 255 => {
+                        self.ascii_code = v as u8;
+                        self.error = None;
+                        Ok(())
+                    }
+                    Ok(_) => {
+                        self.error = Some("Max 255");
+                        Err(())
+                    }
+                    Err(_) => {
+                        self.error = Some("Invalid dec");
+                        Err(())
+                    }
+                }
+            }
+        }
+    }
+}
+
+fn format_ascii_glyph(code: u8) -> String {
+    if let Some(name) = ascii_control_name(code) {
+        format!("<{name}>")
+    } else if code == b' ' {
+        " ".into()
+    } else if code.is_ascii_graphic() {
+        (code as char).to_string()
+    } else {
+        // Latin-1 printable or other
+        match char::from_u32(code as u32) {
+            Some(c) if !c.is_control() => c.to_string(),
+            _ => format!("<{code:02X}>"),
+        }
+    }
+}
+
+fn ascii_control_name(code: u8) -> Option<&'static str> {
+    Some(match code {
+        0x00 => "NUL",
+        0x01 => "SOH",
+        0x02 => "STX",
+        0x03 => "ETX",
+        0x04 => "EOT",
+        0x05 => "ENQ",
+        0x06 => "ACK",
+        0x07 => "BEL",
+        0x08 => "BS",
+        0x09 => "TAB",
+        0x0A => "LF",
+        0x0B => "VT",
+        0x0C => "FF",
+        0x0D => "CR",
+        0x0E => "SO",
+        0x0F => "SI",
+        0x10 => "DLE",
+        0x11 => "DC1",
+        0x12 => "DC2",
+        0x13 => "DC3",
+        0x14 => "DC4",
+        0x15 => "NAK",
+        0x16 => "SYN",
+        0x17 => "ETB",
+        0x18 => "CAN",
+        0x19 => "EM",
+        0x1A => "SUB",
+        0x1B => "ESC",
+        0x1C => "FS",
+        0x1D => "GS",
+        0x1E => "RS",
+        0x1F => "US",
+        0x7F => "DEL",
+        _ => return None,
+    })
+}
+
+/// Best rational approximation of `x` with num, den ∈ [0..=max_val], den ≥ 1.
+/// Stops early when relative error ≤ `max_rel_err` (smallest such convergent preferred).
+pub fn approximate_ratio(x: f64, max_val: u32, max_rel_err: f64) -> Option<RatioResult> {
+    if !x.is_finite() {
+        return None;
+    }
+    if x == 0.0 {
+        return Some(RatioResult {
+            num: 0,
+            den: 1,
+            approx: 0.0,
+            rel_error: 0.0,
+            exact: true,
+        });
+    }
+
+    let x = x.abs();
+    let max_val = max_val as u64;
+
+    let mut best = RatioResult {
+        num: 0,
+        den: 1,
+        approx: 0.0,
+        rel_error: 1.0,
+        exact: false,
+    };
+
+    let consider = |n: u64, d: u64, best: &mut RatioResult| {
+        if d == 0 || d > max_val || n > max_val {
+            return;
+        }
+        let approx = n as f64 / d as f64;
+        let rel = if x == 0.0 {
+            0.0
+        } else {
+            (approx - x).abs() / x
+        };
+        let exact = (approx - x).abs() <= f64::EPSILON * x.max(1.0) * 4.0;
+        if rel < best.rel_error
+            || ((rel - best.rel_error).abs() < 1e-18 && d < best.den as u64)
+            || ((rel - best.rel_error).abs() < 1e-18 && d == best.den as u64 && n < best.num as u64)
+        {
+            *best = RatioResult {
+                num: n as u32,
+                den: d as u32,
+                approx,
+                rel_error: rel,
+                exact,
+            };
+        }
+    };
+
+    // Continued fraction: h₋₂=0,k₋₂=1 ; h₋₁=1,k₋₁=0
+    let mut h2 = 0u64;
+    let mut k2 = 1u64;
+    let mut h1 = 1u64;
+    let mut k1 = 0u64;
+
+    let mut remaining = x;
+    for _ in 0..64 {
+        if best.rel_error <= max_rel_err {
+            break;
+        }
+        let a = remaining.floor() as u64;
+        let t_start = if a == 0 { 0 } else { 1 };
+        let mut last_h = h1;
+        let mut last_k = k1;
+        let mut fitted = false;
+
+        for t in t_start..=a {
+            let Some(hn) = h1.checked_mul(t).and_then(|v| v.checked_add(h2)) else {
+                fitted = false;
+                break;
+            };
+            let Some(kn) = k1.checked_mul(t).and_then(|v| v.checked_add(k2)) else {
+                fitted = false;
+                break;
+            };
+            if hn > max_val || kn > max_val {
+                let mut lo = t_start;
+                let mut hi = t.saturating_sub(1);
+                while lo < hi {
+                    let mid = (lo + hi + 1) / 2;
+                    let ok = h1
+                        .checked_mul(mid)
+                        .and_then(|v| v.checked_add(h2))
+                        .zip(k1.checked_mul(mid).and_then(|v| v.checked_add(k2)))
+                        .is_some_and(|(h, k)| h <= max_val && k <= max_val);
+                    if ok {
+                        lo = mid;
+                    } else {
+                        hi = mid - 1;
+                    }
+                }
+                if a == 0 || lo >= t_start {
+                    if let (Some(hn), Some(kn)) = (
+                        h1.checked_mul(lo).and_then(|v| v.checked_add(h2)),
+                        k1.checked_mul(lo).and_then(|v| v.checked_add(k2)),
+                    ) {
+                        if kn > 0 && hn <= max_val && kn <= max_val {
+                            consider(hn, kn, &mut best);
+                        }
+                    }
+                }
+                fitted = false;
+                break;
+            }
+            consider(hn, kn, &mut best);
+            last_h = hn;
+            last_k = kn;
+            fitted = true;
+            if best.rel_error <= max_rel_err {
+                break;
+            }
+        }
+
+        if best.rel_error <= max_rel_err {
+            break;
+        }
+
+        if fitted {
+            h2 = h1;
+            k2 = k1;
+            h1 = last_h;
+            k1 = last_k;
+        } else {
+            break;
+        }
+
+        let frac = remaining - a as f64;
+        if frac <= 1e-18 {
+            break;
+        }
+        remaining = 1.0 / frac;
+    }
+
+    Some(best)
+}
+
+fn parse_word(s: &str) -> Result<u16, ()> {
+    let cleaned: String = s.chars().filter(|c| c.is_ascii_hexdigit()).collect();
+    if cleaned.is_empty() {
+        return Ok(0);
+    }
+    u16::from_str_radix(&cleaned, 16).map_err(|_| ())
+}
+
+fn format_float(v: f32) -> String {
+    if !v.is_finite() {
+        return if v.is_nan() {
+            "NaN".into()
+        } else if v.is_sign_negative() {
+            "-Inf".into()
+        } else {
+            "Inf".into()
+        };
+    }
+    let s = format!("{v}");
+    s
+}
+
+/// IEEE float bytes in natural order A B C D (big-endian bit pattern),
+/// then rearrange into two register words for the selected endian.
+pub fn float_to_words(f: f32, endian: Endian) -> (u16, u16) {
+    let abcd = f.to_be_bytes(); // [A, B, C, D]
+    let wire = match endian {
+        Endian::AbCd => abcd,
+        Endian::CdAb => [abcd[2], abcd[3], abcd[0], abcd[1]],
+        Endian::BaDc => [abcd[1], abcd[0], abcd[3], abcd[2]],
+        Endian::DcBa => [abcd[3], abcd[2], abcd[1], abcd[0]],
+    };
+    let w0 = u16::from_be_bytes([wire[0], wire[1]]);
+    let w1 = u16::from_be_bytes([wire[2], wire[3]]);
+    (w0, w1)
+}
+
+pub fn words_to_float(w0: u16, w1: u16, endian: Endian) -> f32 {
+    let a = w0.to_be_bytes();
+    let b = w1.to_be_bytes();
+    let wire = [a[0], a[1], b[0], b[1]];
+    let abcd = match endian {
+        Endian::AbCd => wire,
+        Endian::CdAb => [wire[2], wire[3], wire[0], wire[1]],
+        Endian::BaDc => [wire[1], wire[0], wire[3], wire[2]],
+        Endian::DcBa => [wire[3], wire[2], wire[1], wire[0]],
+    };
+    f32::from_be_bytes(abcd)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn one_point_zero_abcd() {
+        let (w0, w1) = float_to_words(1.0, Endian::AbCd);
+        assert_eq!(w0, 0x3F80);
+        assert_eq!(w1, 0x0000);
+        assert_eq!(words_to_float(w0, w1, Endian::AbCd), 1.0);
+    }
+
+    #[test]
+    fn one_point_zero_dcba() {
+        let (w0, w1) = float_to_words(1.0, Endian::DcBa);
+        assert_eq!(w0, 0x0000);
+        assert_eq!(w1, 0x803F);
+        assert_eq!(words_to_float(w0, w1, Endian::DcBa), 1.0);
+    }
+
+    #[test]
+    fn one_point_zero_cdab() {
+        let (w0, w1) = float_to_words(1.0, Endian::CdAb);
+        assert_eq!(w0, 0x0000);
+        assert_eq!(w1, 0x3F80);
+        assert_eq!(words_to_float(w0, w1, Endian::CdAb), 1.0);
+    }
+
+    #[test]
+    fn roundtrip_all_endians() {
+        let samples = [0.0f32, -1.0, 3.1415927, 12345.678, f32::MIN_POSITIVE];
+        for e in Endian::all() {
+            for &f in &samples {
+                let (w0, w1) = float_to_words(f, e);
+                let back = words_to_float(w0, w1, e);
+                assert_eq!(back.to_bits(), f.to_bits(), "endian {:?}", e);
+            }
+        }
+    }
+
+    #[test]
+    fn pi_word_ratio() {
+        let r = approximate_ratio(std::f64::consts::PI, 65535, 1e-6).unwrap();
+        assert_eq!((r.num, r.den), (355, 113));
+    }
+
+    #[test]
+    fn half_byte_ratio() {
+        let r = approximate_ratio(0.5, 255, 1e-9).unwrap();
+        assert_eq!((r.num, r.den), (1, 2));
+    }
+
+    #[test]
+    fn gear_ratio_example() {
+        // 17/23 electronic gear style
+        let r = approximate_ratio(17.0 / 23.0, 255, 1e-9).unwrap();
+        assert_eq!((r.num, r.den), (17, 23));
+    }
+
+    #[test]
+    fn ascii_char_to_codes() {
+        let mut c = Converter::new();
+        c.set_panel(ConvPanel::Ascii);
+        c.set_active(ConvField::AsciiChar);
+        c.input_char('A');
+        assert_eq!(c.ascii_code(), 0x41);
+        assert_eq!(c.ascii_hex_text(), "41");
+        assert_eq!(c.ascii_dec_text(), "65");
+    }
+
+    #[test]
+    fn ascii_hex_to_char() {
+        let mut c = Converter::new();
+        c.set_panel(ConvPanel::Ascii);
+        c.set_active(ConvField::AsciiHex);
+        c.input_char('4');
+        c.input_char('1');
+        assert_eq!(c.ascii_code(), b'A');
+        assert_eq!(c.ascii_char_text(), "A");
+    }
+}

src/crc.rs

@@ -0,0 +1,168 @@
+//! Modbus RTU CRC-16 and Modbus ASCII LRC.
+
+#[derive(Debug, Clone, Default)]
+pub struct CrcTool {
+    /// Raw text from the input field (hex bytes, spaces optional).
+    input: String,
+}
+
+#[derive(Debug, Clone)]
+pub struct CrcView {
+    pub input: String,
+    pub parsed_hex: String,
+    pub byte_count: usize,
+    pub rtu_crc_lo_hi: String,
+    pub rtu_crc_word: String,
+    pub rtu_frame: String,
+    pub ascii_lrc: String,
+    pub ascii_frame: String,
+    pub error: String,
+}
+
+impl CrcTool {
+    pub fn new() -> Self {
+        Self {
+            input: "01 03 00 00 00 0A".into(),
+        }
+    }
+
+    pub fn input(&self) -> &str {
+        &self.input
+    }
+
+    pub fn set_input(&mut self, text: impl Into<String>) {
+        self.input = text.into();
+    }
+
+    pub fn view(&self) -> CrcView {
+        match parse_hex_bytes(&self.input) {
+            Ok(bytes) => {
+                let crc = modbus_crc16(&bytes);
+                let lo = (crc & 0xFF) as u8;
+                let hi = (crc >> 8) as u8;
+                let lrc = modbus_lrc(&bytes);
+
+                let parsed_hex = format_bytes(&bytes);
+                let mut frame = bytes.clone();
+                frame.push(lo);
+                frame.push(hi);
+
+                let ascii_payload: String = bytes.iter().map(|b| format!("{b:02X}")).collect();
+                let ascii_frame = format!(":{ascii_payload}{lrc:02X}\\r\\n");
+
+                CrcView {
+                    input: self.input.clone(),
+                    parsed_hex,
+                    byte_count: bytes.len(),
+                    rtu_crc_lo_hi: format!("{lo:02X} {hi:02X}"),
+                    rtu_crc_word: format!("0x{crc:04X}"),
+                    rtu_frame: format_bytes(&frame),
+                    ascii_lrc: format!("{lrc:02X}"),
+                    ascii_frame,
+                    error: String::new(),
+                }
+            }
+            Err(e) => CrcView {
+                input: self.input.clone(),
+                parsed_hex: String::new(),
+                byte_count: 0,
+                rtu_crc_lo_hi: "—".into(),
+                rtu_crc_word: "—".into(),
+                rtu_frame: "—".into(),
+                ascii_lrc: "—".into(),
+                ascii_frame: "—".into(),
+                error: e.into(),
+            },
+        }
+    }
+}
+
+/// Modbus RTU CRC-16 (poly 0xA001, init 0xFFFF). Returned value is host u16;
+/// on the wire it is sent low-byte first.
+pub fn modbus_crc16(data: &[u8]) -> u16 {
+    let mut crc = 0xFFFFu16;
+    for &b in data {
+        crc ^= u16::from(b);
+        for _ in 0..8 {
+            if crc & 1 != 0 {
+                crc = (crc >> 1) ^ 0xA001;
+            } else {
+                crc >>= 1;
+            }
+        }
+    }
+    crc
+}
+
+/// Modbus ASCII LRC: two's complement of the sum of bytes.
+pub fn modbus_lrc(data: &[u8]) -> u8 {
+    let sum = data.iter().fold(0u8, |acc, &b| acc.wrapping_add(b));
+    (!sum).wrapping_add(1)
+}
+
+fn format_bytes(data: &[u8]) -> String {
+    data.iter()
+        .map(|b| format!("{b:02X}"))
+        .collect::<Vec<_>>()
+        .join(" ")
+}
+
+/// Accepts `01 03 00 00`, `01-03-00`, `0x01,0x03`, or continuous `01030000`.
+fn parse_hex_bytes(text: &str) -> Result<Vec<u8>, &'static str> {
+    let cleaned: String = text
+        .chars()
+        .filter(|c| c.is_ascii_hexdigit())
+        .collect::<String>()
+        .to_ascii_uppercase();
+
+    if cleaned.is_empty() {
+        return Ok(Vec::new());
+    }
+    if cleaned.len() % 2 != 0 {
+        return Err("Odd number of hex digits");
+    }
+
+    let mut out = Vec::with_capacity(cleaned.len() / 2);
+    let bytes = cleaned.as_bytes();
+    for i in (0..bytes.len()).step_by(2) {
+        let hi = from_hex(bytes[i])?;
+        let lo = from_hex(bytes[i + 1])?;
+        out.push((hi << 4) | lo);
+    }
+    Ok(out)
+}
+
+fn from_hex(b: u8) -> Result<u8, &'static str> {
+    match b {
+        b'0'..=b'9' => Ok(b - b'0'),
+        b'A'..=b'F' => Ok(b - b'A' + 10),
+        b'a'..=b'f' => Ok(b - b'a' + 10),
+        _ => Err("Invalid hex"),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn known_modbus_crc() {
+        // 01 03 00 00 00 0A → CRC lo hi = C5 CD
+        let data = [0x01u8, 0x03, 0x00, 0x00, 0x00, 0x0A];
+        let crc = modbus_crc16(&data);
+        assert_eq!(crc & 0xFF, 0xC5);
+        assert_eq!(crc >> 8, 0xCD);
+    }
+
+    #[test]
+    fn known_modbus_lrc() {
+        let data = [0x01u8, 0x03, 0x00, 0x00, 0x00, 0x0A];
+        assert_eq!(modbus_lrc(&data), 0xF2);
+    }
+
+    #[test]
+    fn parse_spaced() {
+        let b = parse_hex_bytes("01 03 00 00 00 0A").unwrap();
+        assert_eq!(b, vec![0x01, 0x03, 0x00, 0x00, 0x00, 0x0A]);
+    }
+}

src/engine.rs

@@ -0,0 +1,425 @@
+//! Calculator logic (standard / Windows-like).
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Op {
+    Add,
+    Sub,
+    Mul,
+    Div,
+}
+
+impl Op {
+    pub fn symbol(self) -> &'static str {
+        match self {
+            Op::Add => "+",
+            Op::Sub => "−",
+            Op::Mul => "×",
+            Op::Div => "÷",
+        }
+    }
+
+    fn apply(self, a: f64, b: f64) -> Result<f64, CalcError> {
+        let r = match self {
+            Op::Add => a + b,
+            Op::Sub => a - b,
+            Op::Mul => a * b,
+            Op::Div => {
+                if b == 0.0 {
+                    return Err(CalcError::DivByZero);
+                }
+                a / b
+            }
+        };
+        if !r.is_finite() {
+            Err(CalcError::Overflow)
+        } else {
+            Ok(r)
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CalcError {
+    DivByZero,
+    Overflow,
+    Invalid,
+}
+
+impl CalcError {
+    pub fn message(self) -> &'static str {
+        match self {
+            CalcError::DivByZero => "Cannot divide by zero",
+            CalcError::Overflow => "Overflow",
+            CalcError::Invalid => "Invalid input",
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Calculator {
+    /// Digits currently being entered (or last result as string).
+    entry: String,
+    /// True while the user is typing a new number.
+    typing: bool,
+    /// Left operand waiting for the next number / equals.
+    pending: Option<f64>,
+    /// Pending binary operator.
+    op: Option<Op>,
+    /// Expression line above the main display (e.g. "12 +").
+    expression: String,
+    /// Last error, if any.
+    error: Option<CalcError>,
+    /// Memory register.
+    memory: f64,
+    /// Whether memory has been set (for UI hint).
+    memory_set: bool,
+}
+
+impl Default for Calculator {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Calculator {
+    pub fn new() -> Self {
+        Self {
+            entry: "0".into(),
+            typing: false,
+            pending: None,
+            op: None,
+            expression: String::new(),
+            error: None,
+            memory: 0.0,
+            memory_set: false,
+        }
+    }
+
+    pub fn display(&self) -> &str {
+        if let Some(err) = self.error {
+            return err.message();
+        }
+        &self.entry
+    }
+
+    pub fn expression(&self) -> &str {
+        &self.expression
+    }
+
+    pub fn has_memory(&self) -> bool {
+        self.memory_set
+    }
+
+    pub fn clear_all(&mut self) {
+        *self = Self {
+            memory: self.memory,
+            memory_set: self.memory_set,
+            ..Self::new()
+        };
+    }
+
+    pub fn clear_entry(&mut self) {
+        self.error = None;
+        self.entry = "0".into();
+        self.typing = false;
+    }
+
+    pub fn backspace(&mut self) {
+        if self.error.is_some() {
+            self.clear_entry();
+            return;
+        }
+        if !self.typing {
+            return;
+        }
+        self.entry.pop();
+        if self.entry.is_empty() || self.entry == "-" {
+            self.entry = "0".into();
+            self.typing = false;
+        }
+    }
+
+    pub fn input_digit(&mut self, d: char) {
+        debug_assert!(d.is_ascii_digit());
+        if self.error.is_some() {
+            self.clear_all();
+        }
+        if !self.typing {
+            self.entry = d.to_string();
+            self.typing = true;
+            return;
+        }
+        if self.entry == "0" {
+            self.entry = d.to_string();
+        } else if self.entry == "-0" {
+            self.entry = format!("-{d}");
+        } else if digit_count(&self.entry) < 16 {
+            self.entry.push(d);
+        }
+    }
+
+    pub fn input_dot(&mut self) {
+        if self.error.is_some() {
+            self.clear_all();
+        }
+        if !self.typing {
+            self.entry = "0.".into();
+            self.typing = true;
+            return;
+        }
+        if !self.entry.contains('.') {
+            self.entry.push('.');
+        }
+    }
+
+    pub fn negate(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        if let Ok(v) = self.current_value() {
+            self.set_entry(-v);
+            self.typing = true;
+        }
+    }
+
+    pub fn percent(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        let Ok(cur) = self.current_value() else {
+            return;
+        };
+        let result = match (self.pending, self.op) {
+            (Some(a), Some(Op::Add | Op::Sub)) => a * cur / 100.0,
+            _ => cur / 100.0,
+        };
+        self.set_entry(result);
+        self.typing = false;
+    }
+
+    pub fn reciprocal(&mut self) {
+        self.unary(|x| {
+            if x == 0.0 {
+                Err(CalcError::DivByZero)
+            } else {
+                Ok(1.0 / x)
+            }
+        });
+    }
+
+    pub fn square(&mut self) {
+        self.unary(|x| {
+            let r = x * x;
+            if r.is_finite() {
+                Ok(r)
+            } else {
+                Err(CalcError::Overflow)
+            }
+        });
+    }
+
+    pub fn sqrt(&mut self) {
+        self.unary(|x| {
+            if x < 0.0 {
+                Err(CalcError::Invalid)
+            } else {
+                Ok(x.sqrt())
+            }
+        });
+    }
+
+    pub fn set_op(&mut self, op: Op) {
+        if self.error.is_some() {
+            return;
+        }
+        if let Err(e) = self.commit_pending() {
+            self.fail(e);
+            return;
+        }
+        let Ok(v) = self.current_value() else {
+            return;
+        };
+        self.pending = Some(v);
+        self.op = Some(op);
+        self.expression = format!("{} {}", format_number(v), op.symbol());
+        self.typing = false;
+    }
+
+    pub fn equals(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        let Some(op) = self.op else {
+            self.expression.clear();
+            self.typing = false;
+            return;
+        };
+        let Ok(b) = self.current_value() else {
+            return;
+        };
+        let a = self.pending.unwrap_or(b);
+        match op.apply(a, b) {
+            Ok(r) => {
+                self.expression = format!(
+                    "{} {} {} =",
+                    format_number(a),
+                    op.symbol(),
+                    format_number(b)
+                );
+                self.set_entry(r);
+                self.pending = None;
+                self.op = None;
+                self.typing = false;
+            }
+            Err(e) => self.fail(e),
+        }
+    }
+
+    // --- Memory ---
+
+    pub fn memory_clear(&mut self) {
+        self.memory = 0.0;
+        self.memory_set = false;
+    }
+
+    pub fn memory_recall(&mut self) {
+        if self.error.is_some() {
+            self.clear_all();
+        }
+        self.set_entry(self.memory);
+        self.typing = false;
+    }
+
+    pub fn memory_add(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        if let Ok(v) = self.current_value() {
+            self.memory += v;
+            self.memory_set = true;
+            self.typing = false;
+        }
+    }
+
+    pub fn memory_sub(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        if let Ok(v) = self.current_value() {
+            self.memory -= v;
+            self.memory_set = true;
+            self.typing = false;
+        }
+    }
+
+    pub fn memory_store(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        if let Ok(v) = self.current_value() {
+            self.memory = v;
+            self.memory_set = true;
+            self.typing = false;
+        }
+    }
+
+    // --- internals ---
+
+    fn unary(&mut self, f: impl FnOnce(f64) -> Result<f64, CalcError>) {
+        if self.error.is_some() {
+            return;
+        }
+        let Ok(v) = self.current_value() else {
+            return;
+        };
+        match f(v) {
+            Ok(r) => {
+                self.expression.clear();
+                self.set_entry(r);
+                self.typing = false;
+            }
+            Err(e) => self.fail(e),
+        }
+    }
+
+    fn commit_pending(&mut self) -> Result<(), CalcError> {
+        let (Some(a), Some(op)) = (self.pending, self.op) else {
+            return Ok(());
+        };
+        if !self.typing {
+            return Ok(());
+        }
+        let b = self.current_value()?;
+        let r = op.apply(a, b)?;
+        self.set_entry(r);
+        self.pending = Some(r);
+        self.op = None;
+        Ok(())
+    }
+
+    fn current_value(&self) -> Result<f64, CalcError> {
+        self.entry
+            .parse::<f64>()
+            .map_err(|_| CalcError::Invalid)
+    }
+
+    fn set_entry(&mut self, v: f64) {
+        self.entry = format_number(v);
+        self.error = None;
+    }
+
+    fn fail(&mut self, e: CalcError) {
+        self.error = Some(e);
+        self.pending = None;
+        self.op = None;
+        self.expression.clear();
+        self.typing = false;
+    }
+}
+
+fn digit_count(s: &str) -> usize {
+    s.chars().filter(|c| c.is_ascii_digit()).count()
+}
+
+fn format_number(v: f64) -> String {
+    if !v.is_finite() {
+        return "0".into();
+    }
+    // Prefer integer display when close enough.
+    if v.fract().abs() < 1e-12 && v.abs() < 1e15 {
+        return format!("{}", v as i64);
+    }
+    let s = format!("{:.12}", v);
+    let s = s.trim_end_matches('0').trim_end_matches('.').to_string();
+    if s.is_empty() || s == "-" {
+        "0".into()
+    } else {
+        s
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn basic_add() {
+        let mut c = Calculator::new();
+        c.input_digit('1');
+        c.input_digit('2');
+        c.set_op(Op::Add);
+        c.input_digit('3');
+        c.equals();
+        assert_eq!(c.display(), "15");
+    }
+
+    #[test]
+    fn div_by_zero() {
+        let mut c = Calculator::new();
+        c.input_digit('1');
+        c.set_op(Op::Div);
+        c.input_digit('0');
+        c.equals();
+        assert!(c.display().contains("zero"));
+    }
+}

src/main.rs

@@ -0,0 +1,370 @@
+// Hide the extra console window on Windows GUI builds.
+#![cfg_attr(all(windows, not(debug_assertions)), windows_subsystem = "windows")]
+
+mod convert;
+mod crc;
+mod engine;
+mod programmer;
+
+use std::cell::RefCell;
+use std::rc::Rc;
+
+use convert::{ConvField, ConvPanel, Converter, Endian, RatioWidth};
+use crc::CrcTool;
+use engine::{Calculator, Op};
+use programmer::{Base, ProgOp, Programmer};
+use slint::{ComponentHandle, ModelRc, VecModel};
+
+slint::include_modules!();
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum Mode {
+    Standard,
+    Programmer,
+    Convert,
+    Crc,
+}
+
+struct State {
+    mode: Mode,
+    std: Calculator,
+    prog: Programmer,
+    conv: Converter,
+    crc: CrcTool,
+    show_bits: bool,
+    win_profile: u32,
+}
+
+impl Default for State {
+    fn default() -> Self {
+        Self {
+            mode: Mode::Standard,
+            std: Calculator::new(),
+            prog: Programmer::new(),
+            conv: Converter::new(),
+            crc: CrcTool::new(),
+            show_bits: true,
+            win_profile: u32::MAX,
+        }
+    }
+}
+
+fn main() -> Result<(), slint::PlatformError> {
+    // Platform must exist first — calling set_xdg_app_id before AppWindow::new
+    // returns NoPlatform and the Wayland app_id stays unset (KDE shows the "W" icon).
+    let ui = AppWindow::new()?;
+    // Must match the .desktop basename (rcalc.desktop → "rcalc"), before show/run.
+    slint::set_xdg_app_id("rcalc")?;
+
+    let state = Rc::new(RefCell::new(State::default()));
+
+    refresh(&ui, &mut state.borrow_mut());
+
+    let ui_weak = ui.as_weak();
+    let state_keys = state.clone();
+    ui.on_key_pressed(move |id| {
+        let mut s = state_keys.borrow_mut();
+        handle_key(&mut s, id.as_str());
+        if let Some(ui) = ui_weak.upgrade() {
+            refresh(&ui, &mut s);
+        }
+    });
+
+    let ui_weak = ui.as_weak();
+    let state_crc = state.clone();
+    ui.on_crc_edited(move |text| {
+        let mut s = state_crc.borrow_mut();
+        s.crc.set_input(text.as_str());
+        if let Some(ui) = ui_weak.upgrade() {
+            apply_crc_results(&ui, &s);
+        }
+    });
+
+    ui.run()
+}
+
+fn bit_row_model(row: &[(bool, u32)]) -> ModelRc<BitInfo> {
+    let items: Vec<BitInfo> = row
+        .iter()
+        .map(|(on, idx)| BitInfo {
+            value: *on,
+            index: *idx as i32,
+        })
+        .collect();
+    ModelRc::new(VecModel::from(items))
+}
+
+fn window_profile(state: &State) -> u32 {
+    let mode = match state.mode {
+        Mode::Standard => 0,
+        Mode::Programmer => 1,
+        Mode::Convert => 2,
+        Mode::Crc => 3,
+    };
+    let bits = if state.show_bits {
+        state.prog.word_size().bits()
+    } else {
+        0
+    };
+    let panel = match state.conv.panel() {
+        ConvPanel::Words => 0,
+        ConvPanel::Ratio => 1,
+        ConvPanel::Ascii => 2,
+    };
+    mode * 1000 + bits * 10 + panel
+}
+
+fn fit_window(ui: &AppWindow, state: &mut State) {
+    let profile = window_profile(state);
+    if state.win_profile == profile {
+        return;
+    }
+    state.win_profile = profile;
+
+    let (w, h) = match state.mode {
+        Mode::Standard => (340.0, 560.0),
+        Mode::Programmer => {
+            let bit_h = if state.show_bits {
+                match state.prog.word_size().bits() {
+                    64 => 120.0,
+                    32 => 64.0,
+                    16 => 36.0,
+                    _ => 36.0,
+                }
+            } else {
+                0.0
+            };
+            (420.0, 720.0 + bit_h)
+        }
+        Mode::Convert => (420.0, 820.0),
+        Mode::Crc => (460.0, 560.0),
+    };
+    ui.window()
+        .set_size(slint::LogicalSize::new(w as f32, h as f32));
+}
+
+fn apply_crc_results(ui: &AppWindow, state: &State) {
+    let v = state.crc.view();
+    ui.set_crc_parsed(v.parsed_hex.into());
+    ui.set_crc_count(v.byte_count.to_string().into());
+    ui.set_crc_rtu_bytes(v.rtu_crc_lo_hi.into());
+    ui.set_crc_rtu_word(v.rtu_crc_word.into());
+    ui.set_crc_rtu_frame(v.rtu_frame.into());
+    ui.set_crc_ascii_lrc(v.ascii_lrc.into());
+    ui.set_crc_ascii_frame(v.ascii_frame.into());
+    ui.set_crc_error(v.error.into());
+}
+
+fn refresh(ui: &AppWindow, state: &mut State) {
+    ui.set_mode(match state.mode {
+        Mode::Standard => 0,
+        Mode::Programmer => 1,
+        Mode::Convert => 2,
+        Mode::Crc => 3,
+    });
+
+    fit_window(ui, state);
+
+    match state.mode {
+        Mode::Standard => {
+            ui.set_display_text(state.std.display().into());
+            ui.set_expression_text(state.std.expression().into());
+            ui.set_has_memory(state.std.has_memory());
+        }
+        Mode::Programmer => {
+            ui.set_display_text(state.prog.display().into());
+            ui.set_expression_text(state.prog.expression().into());
+            ui.set_has_memory(false);
+            ui.set_hex_text(state.prog.hex_text().into());
+            ui.set_dec_text(state.prog.dec_text().into());
+            ui.set_oct_text(state.prog.oct_text().into());
+            ui.set_bin_text(state.prog.bin_text().into());
+            ui.set_active_base(match state.prog.base() {
+                Base::Hex => 0,
+                Base::Dec => 1,
+                Base::Oct => 2,
+                Base::Bin => 3,
+            });
+            ui.set_word_size_label(state.prog.word_size().label().into());
+            ui.set_show_bits(state.show_bits);
+
+            let rows = state.prog.bit_rows();
+            ui.set_bit_row_count(rows.len() as i32);
+            ui.set_bit_row0(bit_row_model(rows.first().map(|r| r.as_slice()).unwrap_or(&[])));
+            ui.set_bit_row1(bit_row_model(rows.get(1).map(|r| r.as_slice()).unwrap_or(&[])));
+            ui.set_bit_row2(bit_row_model(rows.get(2).map(|r| r.as_slice()).unwrap_or(&[])));
+            ui.set_bit_row3(bit_row_model(rows.get(3).map(|r| r.as_slice()).unwrap_or(&[])));
+        }
+        Mode::Convert => {
+            ui.set_conv_panel(match state.conv.panel() {
+                ConvPanel::Words => 0,
+                ConvPanel::Ratio => 1,
+                ConvPanel::Ascii => 2,
+            });
+            ui.set_conv_endian(state.conv.endian_index());
+            ui.set_conv_active(match state.conv.active() {
+                ConvField::Float | ConvField::AsciiChar => 0,
+                ConvField::Word0 | ConvField::AsciiHex => 1,
+                ConvField::Word1 | ConvField::AsciiDec => 2,
+            });
+            ui.set_conv_float(state.conv.float_text().into());
+            ui.set_conv_word0(state.conv.word0_text().into());
+            ui.set_conv_word1(state.conv.word1_text().into());
+            ui.set_conv_bytes(state.conv.wire_bytes_text().into());
+            ui.set_conv_ieee(state.conv.ieee_hex_text().into());
+            ui.set_conv_error(state.conv.error().unwrap_or("").into());
+            ui.set_ratio_width(match state.conv.ratio_width() {
+                RatioWidth::Byte => 0,
+                RatioWidth::Word => 1,
+            });
+            ui.set_ratio_precision(state.conv.precision_text().into());
+            ui.set_ratio_num(state.conv.ratio_num_text().into());
+            ui.set_ratio_den(state.conv.ratio_den_text().into());
+            ui.set_ratio_frac(state.conv.ratio_frac_text().into());
+            ui.set_ratio_approx(state.conv.ratio_approx_text().into());
+            ui.set_ratio_error(state.conv.ratio_error_text().into());
+            ui.set_ascii_char(state.conv.ascii_char_text().into());
+            ui.set_ascii_hex(state.conv.ascii_hex_text().into());
+            ui.set_ascii_dec(state.conv.ascii_dec_text().into());
+            ui.set_ascii_name(state.conv.ascii_name_text().into());
+        }
+        Mode::Crc => {
+            ui.set_crc_input(state.crc.input().into());
+            apply_crc_results(ui, state);
+        }
+    }
+}
+
+fn handle_key(state: &mut State, id: &str) {
+    match id {
+        "mode:std" => {
+            state.mode = Mode::Standard;
+            return;
+        }
+        "mode:prog" => {
+            state.mode = Mode::Programmer;
+            return;
+        }
+        "mode:conv" => {
+            state.mode = Mode::Convert;
+            return;
+        }
+        "mode:crc" => {
+            state.mode = Mode::Crc;
+            return;
+        }
+        _ => {}
+    }
+
+    match state.mode {
+        Mode::Standard => handle_standard(&mut state.std, id),
+        Mode::Programmer => handle_programmer(state, id),
+        Mode::Convert => handle_convert(&mut state.conv, id),
+        Mode::Crc => {}
+    }
+}
+
+fn handle_standard(calc: &mut Calculator, id: &str) {
+    match id {
+        "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" => {
+            calc.input_digit(id.chars().next().unwrap());
+        }
+        "." | "," => calc.input_dot(),
+        "+" => calc.set_op(Op::Add),
+        "-" | "−" => calc.set_op(Op::Sub),
+        "*" | "×" => calc.set_op(Op::Mul),
+        "/" | "÷" => calc.set_op(Op::Div),
+        "=" => calc.equals(),
+        "%" => calc.percent(),
+        "CE" => calc.clear_entry(),
+        "C" => calc.clear_all(),
+        "BS" => calc.backspace(),
+        "1/x" => calc.reciprocal(),
+        "x2" => calc.square(),
+        "sqrt" => calc.sqrt(),
+        "neg" => calc.negate(),
+        "MC" => calc.memory_clear(),
+        "MR" => calc.memory_recall(),
+        "M+" => calc.memory_add(),
+        "M-" => calc.memory_sub(),
+        "MS" => calc.memory_store(),
+        _ => {}
+    }
+}
+
+fn handle_programmer(state: &mut State, id: &str) {
+    if id == "bits" {
+        state.show_bits = !state.show_bits;
+        return;
+    }
+
+    if let Some(rest) = id.strip_prefix("bit:") {
+        if let Ok(bit) = rest.parse::<u32>() {
+            state.prog.toggle_bit(bit);
+        }
+        return;
+    }
+
+    let calc = &mut state.prog;
+    match id {
+        "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" | "A" | "B" | "C" | "D"
+        | "E" | "F" | "a" | "b" | "c" | "d" | "e" | "f" => {
+            calc.input_digit(id.chars().next().unwrap());
+        }
+        "base:hex" => calc.set_base(Base::Hex),
+        "base:dec" => calc.set_base(Base::Dec),
+        "base:oct" => calc.set_base(Base::Oct),
+        "base:bin" => calc.set_base(Base::Bin),
+        "word" => calc.cycle_word_size(),
+        "+" => calc.set_op(ProgOp::Add),
+        "-" | "−" => calc.set_op(ProgOp::Sub),
+        "*" | "×" => calc.set_op(ProgOp::Mul),
+        "/" | "÷" => calc.set_op(ProgOp::Div),
+        "%" => calc.set_op(ProgOp::Mod),
+        "AND" => calc.set_op(ProgOp::And),
+        "OR" => calc.set_op(ProgOp::Or),
+        "XOR" => calc.set_op(ProgOp::Xor),
+        "NAND" => calc.set_op(ProgOp::Nand),
+        "NOR" => calc.set_op(ProgOp::Nor),
+        "Lsh" => calc.set_op(ProgOp::Lsh),
+        "Rsh" => calc.set_op(ProgOp::Rsh),
+        "NOT" => calc.not(),
+        "=" => calc.equals(),
+        "CE" => calc.clear_entry(),
+        "clear" => calc.clear_all(),
+        "BS" => calc.backspace(),
+        "neg" => calc.negate(),
+        _ => {}
+    }
+}
+
+fn handle_convert(conv: &mut Converter, id: &str) {
+    match id {
+        "panel:words" => conv.set_panel(ConvPanel::Words),
+        "panel:ratio" => conv.set_panel(ConvPanel::Ratio),
+        "panel:ascii" => conv.set_panel(ConvPanel::Ascii),
+        "endian:0" => conv.set_endian(Endian::AbCd),
+        "endian:1" => conv.set_endian(Endian::CdAb),
+        "endian:2" => conv.set_endian(Endian::BaDc),
+        "endian:3" => conv.set_endian(Endian::DcBa),
+        "rwidth:byte" => conv.set_ratio_width(RatioWidth::Byte),
+        "rwidth:word" => conv.set_ratio_width(RatioWidth::Word),
+        "rprec" => conv.cycle_precision(),
+        "conv:float" => conv.set_active(ConvField::Float),
+        "conv:w0" => conv.set_active(ConvField::Word0),
+        "conv:w1" => conv.set_active(ConvField::Word1),
+        "ascii:char" => conv.set_active(ConvField::AsciiChar),
+        "ascii:hex" => conv.set_active(ConvField::AsciiHex),
+        "ascii:dec" => conv.set_active(ConvField::AsciiDec),
+        "CE" | "clear" => conv.clear_active(),
+        "BS" => conv.backspace(),
+        "neg" => conv.negate_float(),
+        other => {
+            // Single-character input (digits, letters, space, punctuation).
+            let mut chars = other.chars();
+            if let (Some(ch), None) = (chars.next(), chars.next()) {
+                conv.input_char(ch);
+            }
+        }
+    }
+}

src/programmer.rs

@@ -0,0 +1,680 @@
+//! Programmer calculator (Windows-like): integer bases + bitwise ops.
+
+use std::fmt::Write as _;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Base {
+    Hex,
+    Dec,
+    Oct,
+    Bin,
+}
+
+impl Base {
+    pub fn radix(self) -> u32 {
+        match self {
+            Base::Hex => 16,
+            Base::Dec => 10,
+            Base::Oct => 8,
+            Base::Bin => 2,
+        }
+    }
+
+    pub fn label(self) -> &'static str {
+        match self {
+            Base::Hex => "HEX",
+            Base::Dec => "DEC",
+            Base::Oct => "OCT",
+            Base::Bin => "BIN",
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum WordSize {
+    /// 64-bit (signed DEC).
+    Qword,
+    /// 32-bit unsigned (PLC DWORD).
+    Dword,
+    /// 32-bit signed (PLC DINT).
+    Dint,
+    /// 16-bit unsigned (PLC WORD).
+    Word,
+    /// 16-bit signed (PLC INT).
+    Int,
+    /// 8-bit (signed DEC).
+    Byte,
+}
+
+impl WordSize {
+    pub fn bits(self) -> u32 {
+        match self {
+            WordSize::Qword => 64,
+            WordSize::Dword | WordSize::Dint => 32,
+            WordSize::Word | WordSize::Int => 16,
+            WordSize::Byte => 8,
+        }
+    }
+
+    /// Signed two's-complement DEC display (INT / DINT / QWORD / BYTE).
+    pub fn is_signed(self) -> bool {
+        matches!(
+            self,
+            WordSize::Qword | WordSize::Dint | WordSize::Int | WordSize::Byte
+        )
+    }
+
+    pub fn label(self) -> &'static str {
+        match self {
+            WordSize::Qword => "QWORD",
+            WordSize::Dword => "DWORD",
+            WordSize::Dint => "DINT",
+            WordSize::Word => "WORD",
+            WordSize::Int => "INT",
+            WordSize::Byte => "BYTE",
+        }
+    }
+
+    pub fn cycle(self) -> Self {
+        match self {
+            WordSize::Qword => WordSize::Dword,
+            WordSize::Dword => WordSize::Dint,
+            WordSize::Dint => WordSize::Word,
+            WordSize::Word => WordSize::Int,
+            WordSize::Int => WordSize::Byte,
+            WordSize::Byte => WordSize::Qword,
+        }
+    }
+
+    fn mask(self) -> u64 {
+        match self.bits() {
+            64 => u64::MAX,
+            bits => (1u64 << bits) - 1,
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ProgOp {
+    Add,
+    Sub,
+    Mul,
+    Div,
+    Mod,
+    And,
+    Or,
+    Xor,
+    Nand,
+    Nor,
+    Lsh,
+    Rsh,
+}
+
+impl ProgOp {
+    pub fn symbol(self) -> &'static str {
+        match self {
+            ProgOp::Add => "+",
+            ProgOp::Sub => "−",
+            ProgOp::Mul => "×",
+            ProgOp::Div => "÷",
+            ProgOp::Mod => "%",
+            ProgOp::And => "AND",
+            ProgOp::Or => "OR",
+            ProgOp::Xor => "XOR",
+            ProgOp::Nand => "NAND",
+            ProgOp::Nor => "NOR",
+            ProgOp::Lsh => "Lsh",
+            ProgOp::Rsh => "Rsh",
+        }
+    }
+
+    fn apply(self, a: u64, b: u64, size: WordSize) -> Result<u64, ProgError> {
+        let mask = size.mask();
+        let a = a & mask;
+        let b = b & mask;
+        let r = match self {
+            ProgOp::Add => a.wrapping_add(b),
+            ProgOp::Sub => a.wrapping_sub(b),
+            ProgOp::Mul => a.wrapping_mul(b),
+            ProgOp::Div => {
+                if b == 0 {
+                    return Err(ProgError::DivByZero);
+                }
+                a / b
+            }
+            ProgOp::Mod => {
+                if b == 0 {
+                    return Err(ProgError::DivByZero);
+                }
+                a % b
+            }
+            ProgOp::And => a & b,
+            ProgOp::Or => a | b,
+            ProgOp::Xor => a ^ b,
+            ProgOp::Nand => !(a & b),
+            ProgOp::Nor => !(a | b),
+            ProgOp::Lsh => {
+                let sh = (b as u32) % size.bits().max(1);
+                a << sh
+            }
+            ProgOp::Rsh => {
+                let sh = (b as u32) % size.bits().max(1);
+                a >> sh
+            }
+        };
+        Ok(r & mask)
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ProgError {
+    DivByZero,
+    Invalid,
+}
+
+impl ProgError {
+    pub fn message(self) -> &'static str {
+        match self {
+            ProgError::DivByZero => "Cannot divide by zero",
+            ProgError::Invalid => "Invalid input",
+        }
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct Programmer {
+    entry: String,
+    typing: bool,
+    value: u64,
+    pending: Option<u64>,
+    op: Option<ProgOp>,
+    expression: String,
+    error: Option<ProgError>,
+    base: Base,
+    word_size: WordSize,
+}
+
+impl Default for Programmer {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Programmer {
+    pub fn new() -> Self {
+        Self {
+            entry: "0".into(),
+            typing: false,
+            value: 0,
+            pending: None,
+            op: None,
+            expression: String::new(),
+            error: None,
+            base: Base::Dec,
+            word_size: WordSize::Qword,
+        }
+    }
+
+    pub fn base(&self) -> Base {
+        self.base
+    }
+
+    pub fn word_size(&self) -> WordSize {
+        self.word_size
+    }
+
+    pub fn expression(&self) -> &str {
+        &self.expression
+    }
+
+    pub fn display(&self) -> String {
+        if let Some(err) = self.error {
+            return err.message().into();
+        }
+        if self.typing {
+            format_grouped_entry(&self.entry, self.base)
+        } else {
+            format_value(self.value, self.base, self.word_size)
+        }
+    }
+
+    pub fn hex_text(&self) -> String {
+        format_value(self.current_bits(), Base::Hex, self.word_size)
+    }
+
+    pub fn dec_text(&self) -> String {
+        format_value(self.current_bits(), Base::Dec, self.word_size)
+    }
+
+    pub fn oct_text(&self) -> String {
+        format_value(self.current_bits(), Base::Oct, self.word_size)
+    }
+
+    pub fn bin_text(&self) -> String {
+        format_value(self.current_bits(), Base::Bin, self.word_size)
+    }
+
+    /// Bit rows for the clickable bit board (MSB-first within each row).
+    /// Each entry is `(is_set, bit_index)` with `bit_index` counted from LSB = 0.
+    pub fn bit_rows(&self) -> Vec<Vec<(bool, u32)>> {
+        let n = self.word_size.bits();
+        let v = self.current_bits();
+        let cols: u32 = if n <= 8 { 8 } else { 16 };
+        let mut rows = Vec::new();
+        let mut row = Vec::new();
+        for i in (0..n).rev() {
+            row.push(((v >> i) & 1 == 1, i));
+            if row.len() == cols as usize {
+                rows.push(std::mem::take(&mut row));
+            }
+        }
+        if !row.is_empty() {
+            rows.push(row);
+        }
+        rows
+    }
+
+    pub fn toggle_bit(&mut self, bit: u32) {
+        if bit >= self.word_size.bits() {
+            return;
+        }
+        if self.error.is_some() {
+            self.clear_entry();
+        }
+        let v = self.current_bits();
+        self.value = (v ^ (1u64 << bit)) & self.word_size.mask();
+        self.typing = false;
+        self.error = None;
+        self.entry = format_raw(self.value, self.base, self.word_size);
+    }
+
+    pub fn set_base(&mut self, base: Base) {
+        if self.error.is_some() {
+            self.clear_entry();
+        }
+        // Commit typed digits into value when switching bases.
+        if self.typing {
+            if let Ok(v) = parse_entry(&self.entry, self.base) {
+                self.value = v & self.word_size.mask();
+            }
+            self.typing = false;
+        }
+        self.base = base;
+        self.entry = format_raw(self.value, base, self.word_size);
+    }
+
+    pub fn cycle_word_size(&mut self) {
+        if self.typing {
+            if let Ok(v) = parse_entry(&self.entry, self.base) {
+                self.value = v;
+            }
+            self.typing = false;
+        }
+        self.word_size = self.word_size.cycle();
+        self.value &= self.word_size.mask();
+        if let Some(p) = self.pending.as_mut() {
+            *p &= self.word_size.mask();
+        }
+        self.entry = format_raw(self.value, self.base, self.word_size);
+    }
+
+    pub fn clear_all(&mut self) {
+        let base = self.base;
+        let word_size = self.word_size;
+        *self = Self::new();
+        self.base = base;
+        self.word_size = word_size;
+    }
+
+    pub fn clear_entry(&mut self) {
+        self.error = None;
+        self.entry = "0".into();
+        self.value = 0;
+        self.typing = false;
+    }
+
+    pub fn backspace(&mut self) {
+        if self.error.is_some() {
+            self.clear_entry();
+            return;
+        }
+        if !self.typing {
+            return;
+        }
+        self.entry.pop();
+        if self.entry.is_empty() {
+            self.entry = "0".into();
+            self.typing = false;
+            self.value = 0;
+        } else if let Ok(v) = parse_entry(&self.entry, self.base) {
+            self.value = v & self.word_size.mask();
+        }
+    }
+
+    pub fn input_digit(&mut self, ch: char) {
+        let ch = ch.to_ascii_uppercase();
+        if !is_valid_digit(ch, self.base) {
+            return;
+        }
+        if self.error.is_some() {
+            self.clear_all();
+        }
+
+        if !self.typing {
+            self.entry = ch.to_string();
+            self.typing = true;
+        } else if self.entry == "0" {
+            self.entry = ch.to_string();
+        } else {
+            let max_digits = max_digits(self.base, self.word_size);
+            if digit_len(&self.entry) >= max_digits {
+                return;
+            }
+            self.entry.push(ch);
+        }
+
+        match parse_entry(&self.entry, self.base) {
+            Ok(v) => {
+                let masked = v & self.word_size.mask();
+                // Reject overflow beyond word size (except wrapping interpretation of typed hex).
+                if v != masked && self.base != Base::Bin {
+                    self.entry.pop();
+                    if self.entry.is_empty() {
+                        self.entry = "0".into();
+                        self.typing = false;
+                    }
+                    return;
+                }
+                self.value = masked;
+            }
+            Err(_) => {
+                self.entry.pop();
+            }
+        }
+    }
+
+    pub fn negate(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        let v = self.current_bits();
+        self.value = (!v).wrapping_add(1) & self.word_size.mask();
+        self.typing = false;
+        self.entry = format_raw(self.value, self.base, self.word_size);
+    }
+
+    pub fn not(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        let v = self.current_bits();
+        self.value = (!v) & self.word_size.mask();
+        self.expression.clear();
+        self.typing = false;
+        self.entry = format_raw(self.value, self.base, self.word_size);
+    }
+
+    pub fn set_op(&mut self, op: ProgOp) {
+        if self.error.is_some() {
+            return;
+        }
+        if let Err(e) = self.commit_pending() {
+            self.fail(e);
+            return;
+        }
+        let v = self.current_bits();
+        self.pending = Some(v);
+        self.op = Some(op);
+        self.expression = format!(
+            "{} {}",
+            format_value(v, self.base, self.word_size),
+            op.symbol()
+        );
+        self.typing = false;
+        self.entry = format_raw(v, self.base, self.word_size);
+    }
+
+    pub fn equals(&mut self) {
+        if self.error.is_some() {
+            return;
+        }
+        let Some(op) = self.op else {
+            self.expression.clear();
+            self.typing = false;
+            return;
+        };
+        let b = self.current_bits();
+        let a = self.pending.unwrap_or(b);
+        match op.apply(a, b, self.word_size) {
+            Ok(r) => {
+                self.expression = format!(
+                    "{} {} {} =",
+                    format_value(a, self.base, self.word_size),
+                    op.symbol(),
+                    format_value(b, self.base, self.word_size)
+                );
+                self.value = r;
+                self.pending = None;
+                self.op = None;
+                self.typing = false;
+                self.entry = format_raw(r, self.base, self.word_size);
+            }
+            Err(e) => self.fail(e),
+        }
+    }
+
+    fn current_bits(&self) -> u64 {
+        if self.typing {
+            parse_entry(&self.entry, self.base)
+                .unwrap_or(self.value)
+                & self.word_size.mask()
+        } else {
+            self.value & self.word_size.mask()
+        }
+    }
+
+    fn commit_pending(&mut self) -> Result<(), ProgError> {
+        let (Some(a), Some(op)) = (self.pending, self.op) else {
+            return Ok(());
+        };
+        if !self.typing {
+            return Ok(());
+        }
+        let b = self.current_bits();
+        let r = op.apply(a, b, self.word_size)?;
+        self.value = r;
+        self.pending = Some(r);
+        self.op = None;
+        self.entry = format_raw(r, self.base, self.word_size);
+        Ok(())
+    }
+
+    fn fail(&mut self, e: ProgError) {
+        self.error = Some(e);
+        self.pending = None;
+        self.op = None;
+        self.expression.clear();
+        self.typing = false;
+    }
+}
+
+fn is_valid_digit(ch: char, base: Base) -> bool {
+    match base {
+        Base::Bin => matches!(ch, '0' | '1'),
+        Base::Oct => matches!(ch, '0'..='7'),
+        Base::Dec => ch.is_ascii_digit(),
+        Base::Hex => ch.is_ascii_hexdigit(),
+    }
+}
+
+fn digit_len(s: &str) -> usize {
+    s.chars().filter(|c| c.is_ascii_hexdigit()).count()
+}
+
+fn max_digits(base: Base, size: WordSize) -> usize {
+    let bits = size.bits() as f64;
+    match base {
+        Base::Bin => size.bits() as usize,
+        Base::Oct => (bits / 3.0).ceil() as usize,
+        Base::Dec => (bits * std::f64::consts::LN_2 / std::f64::consts::LN_10).ceil() as usize,
+        Base::Hex => (bits / 4.0).ceil() as usize,
+    }
+}
+
+fn parse_entry(entry: &str, base: Base) -> Result<u64, ProgError> {
+    let cleaned: String = entry
+        .chars()
+        .filter(|c| c.is_ascii_hexdigit())
+        .collect();
+    if cleaned.is_empty() {
+        return Ok(0);
+    }
+    u64::from_str_radix(&cleaned, base.radix()).map_err(|_| ProgError::Invalid)
+}
+
+fn format_raw(v: u64, base: Base, size: WordSize) -> String {
+    let v = v & size.mask();
+    match base {
+        Base::Dec => {
+            if size.is_signed() {
+                format!("{}", to_signed(v, size))
+            } else {
+                format!("{v}")
+            }
+        }
+        Base::Hex => format!("{:X}", v),
+        Base::Oct => format!("{:o}", v),
+        Base::Bin => format!("{:b}", v),
+    }
+}
+
+fn format_value(v: u64, base: Base, size: WordSize) -> String {
+    format_grouped_entry(&format_raw(v, base, size), base)
+}
+
+fn format_grouped_entry(raw: &str, base: Base) -> String {
+    // Keep leading minus for signed decimal.
+    let (sign, digits) = if let Some(rest) = raw.strip_prefix('-') {
+        ("-", rest)
+    } else {
+        ("", raw)
+    };
+    let digits: String = digits
+        .chars()
+        .filter(|c| c.is_ascii_hexdigit())
+        .collect::<String>()
+        .to_ascii_uppercase();
+    if digits.is_empty() {
+        return format!("{sign}0");
+    }
+    let group = match base {
+        Base::Bin => 4,
+        Base::Hex | Base::Oct => 4,
+        Base::Dec => 3,
+    };
+    let mut out = String::new();
+    for (i, ch) in digits.chars().rev().enumerate() {
+        if i > 0 && i % group == 0 {
+            out.push(' ');
+        }
+        out.push(ch);
+    }
+    let grouped: String = out.chars().rev().collect();
+    let mut result = String::new();
+    let _ = write!(result, "{sign}{grouped}");
+    result
+}
+
+fn to_signed(v: u64, size: WordSize) -> i64 {
+    let bits = size.bits();
+    if bits == 64 {
+        return v as i64;
+    }
+    let mask = size.mask();
+    let v = v & mask;
+    let sign_bit = 1u64 << (bits - 1);
+    if v & sign_bit != 0 {
+        (v | !mask) as i64
+    } else {
+        v as i64
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn hex_and() {
+        let mut p = Programmer::new();
+        p.set_base(Base::Hex);
+        p.input_digit('F');
+        p.input_digit('F');
+        p.set_op(ProgOp::And);
+        p.input_digit('0');
+        p.input_digit('F');
+        p.equals();
+        assert_eq!(p.current_bits(), 0x0F);
+    }
+
+    #[test]
+    fn simultaneous_bases() {
+        let mut p = Programmer::new();
+        p.input_digit('2');
+        p.input_digit('5');
+        p.input_digit('5');
+        assert_eq!(p.hex_text().replace(' ', ""), "FF");
+        assert_eq!(p.bin_text().replace(' ', ""), "11111111");
+    }
+
+    #[test]
+    fn toggle_bit_flips() {
+        let mut p = Programmer::new();
+        // QWORD → DWORD → DINT → WORD → INT → BYTE
+        for _ in 0..5 {
+            p.cycle_word_size();
+        }
+        assert_eq!(p.word_size(), WordSize::Byte);
+        p.toggle_bit(0);
+        p.toggle_bit(7);
+        assert_eq!(p.current_bits(), 0b1000_0001);
+        p.toggle_bit(0);
+        assert_eq!(p.current_bits(), 0b1000_0000);
+    }
+
+    #[test]
+    fn int_vs_word_dec() {
+        let mut p = Programmer::new();
+        p.set_base(Base::Hex);
+        // → DWORD → DINT → WORD
+        p.cycle_word_size();
+        p.cycle_word_size();
+        p.cycle_word_size();
+        assert_eq!(p.word_size(), WordSize::Word);
+        p.input_digit('F');
+        p.input_digit('F');
+        p.input_digit('F');
+        p.input_digit('F');
+        assert_eq!(p.dec_text().replace(' ', ""), "65535");
+
+        p.cycle_word_size(); // INT
+        assert_eq!(p.word_size(), WordSize::Int);
+        assert_eq!(p.dec_text().replace(' ', ""), "-1");
+    }
+
+    #[test]
+    fn dint_vs_dword_dec() {
+        let mut p = Programmer::new();
+        p.set_base(Base::Hex);
+        p.cycle_word_size(); // DWORD
+        assert_eq!(p.word_size(), WordSize::Dword);
+        for _ in 0..8 {
+            p.input_digit('F');
+        }
+        assert_eq!(p.dec_text().replace(' ', ""), "4294967295");
+
+        p.cycle_word_size(); // DINT
+        assert_eq!(p.word_size(), WordSize::Dint);
+        assert_eq!(p.dec_text().replace(' ', ""), "-1");
+    }
+}