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OpenCalc

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A re-implementation of the Windows 95 calculator.

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- - el-f.png
  - el-g.png
  - el-normal.png
  - en-f.png
  - en-g.png
  - en-normal.png
  - es-f.png
  - es-g.png
  - es-normal.png
  - pt-f.png
  - pt-g.png
  - pt-normal.png
- CALC_EL.CNT
- CALC_EL.HLP
- CALC_EN.CNT
- CALC_EN.HLP
- CALC_ES.CNT
- CALC_ES.HLP
- CALC_PT-BR.CNT
- CALC_PT-BR.HLP
- finance.json
- financial-reference.json
- default.cfg
- - linux.rs
  - mod.rs
  - windows.rs
- - linux.rs
  - mod.rs
  - windows.rs
  - windows_menu_flags.rs
- - linux.rs
  - linux_tests.rs
  - mod.rs
  - windows.rs
- calc.rs
- calculation_log.rs
- errors.rs
- expr.rs
- finance.rs
- flags.rs
- graph.rs
- history.rs
- hp12c.rs
- hp12c_memory.rs
- hp12c_tests.rs
- i18n.rs
- main.rs
- settings.rs
- shortcuts.rs
- tooltip.rs
- check_platform_separation.py
- check_rust_delimiters.py
- financial_help_media.py
- rebuild_help_reference_tables.py
- rebuild_help_row_tables.py
- repad_help_tables.py
- update_help_exp_pi.py
- update_help_financial.py
- update_help_graph_syntax.py
build.bat
build.rs
build.sh
calc.tooltip
calc95.ico
Cargo.lock
Cargo.toml
clean-linux.sh
clean_source.bat
HISTORY.md
hlp-viewer.cfg
hlp-viewer.exe
LICENSE
OpenCalc.cfg
README.md
SOURCE_MANIFEST.sha256
test.bat
VALIDATION.txt

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// repository documentation

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OpenCalc is a reimplementation of the classic Windows 95 Calculator, written from scratch in Rust.

The project preserves the familiar interface and interaction model of the original application while adding correcting old limitations.

## Why OpenCalc?

The Windows 95 Calculator remains a recognizable example of compact and practical interface design.
OpenCalc aims to preserve that experience and improve it.

For the detailed development and compatibility history, see [HISTORY.md](HISTORY.md).

At the same time, it expands the original calculator with features such as improved expression parsing, calculation history, graph plotting, localization, modern keyboard support, and high-DPI rendering.

<img width="1770" height="852" alt="image" src="https://github.com/user-attachments/assets/2f60e2fa-dd7c-4b03-9bce-fee3a6ea8961" />

## Features

## A native reimplementation in Rust
While OpenCalc behaves like the Windows 95 calculator, it contains no legacy code.
This means that it does not depend on legacy libraries and can run reliably on modern systems, while also providing modern features such as Undo/Redo, calculation history, and a graph manager.
So yes, you can run it on Linux natively too!

<img width="2594" height="846" alt="image" src="https://github.com/user-attachments/assets/cfe00db3-28c4-47a0-9922-33281d58488d" />

### Classic calculator interface

- Faithful Windows 95 appearance
- Standard and Scientific modes
- Improved font aliasing
- DPI-aware classic button borders
- Memory operations
- Windows 95-compatible memory entry state (MC/MR/MS/M+ end direct numeric entry, while recalled values remain usable as operands)
- Statistics window
- Configurable decimal separator
- Windows 95-style non-decimal Dword / Word / Byte selector in Scientific mode, with exact 32/16/8-bit low-bit display masks while preserving the full DWORD-wide value
- Radix-correct Hex, Oct and Bin arithmetic and pasted expressions (including digit-only Hex operands and Binary operands in Scientific mode)
- Windows 95-style 13-significant-digit formatting for completed Decimal/F-E results, including classic signed three-column scientific exponents (`e+000` / `e-000`), without restoring the original direct-entry length limit

### Calculation history

The optional History panel records completed calculations and can be shown or hidden from the **View** menu.

History entries automatically follow the selected decimal separator and can be cleared independently from the calculator display.

## Keyboard input

When the main Calculator window is focused, the keyboard can be used directly, similarly to the original Windows Calculator.

Some common shortcuts include:

| Key | Action |
|---|---|
| `0–9` | Enter digits |
| `+`, `-`, `*`, `/` | Arithmetic operations |
| `**` | Exponentiation |
| `Enter` or `=` | Calculate the result |
| `Backspace` | Delete the last digit |
| `Delete` | Clear the current entry |
| `C` or `Esc` | Clear the calculation |
| `Shift+C` | Enter hexadecimal C in Scientific mode |
| `F2` | Scientific: Degrees in Decimal / Dword in Hex, Oct, Bin |
| `F3` | Scientific: Radians in Decimal / Word in Hex, Oct, Bin |
| `F4` | Scientific: Grads in Decimal / Byte in Hex, Oct, Bin |
| `F5` | Scientific: Hexadecimal base |
| `F6` | Scientific: Decimal base |
| `F7` | Scientific: Octal base |
| `F8` | Scientific: Binary base |
| `F9` | Change the sign |
| `Ctrl+Insert` | Copy |
| `Shift+Insert` | Paste an expression |

Scientific mode also supports the original single-key function shortcuts.
In Standard mode, F2-F8 do not change hidden Scientific selectors; the calculator remains Decimal, matching the Win95 dispatcher.

Use **Settings... → Keyboard Shortcuts** to select an action and click **Press key for [action]** to record a replacement key or Ctrl/Shift combination. You can also edit the shortcut field, separating alternatives with commas; use the names Plus and Comma for those punctuation keys. A blank field disables that action's keyboard bindings. The **Search shortcuts** box jumps directly to an action by name, internal ID, or current key assignment.

Shortcut presets are plain-text `.cfg` files in the `shortcuts/` directory beside OpenCalc. The shipped default preset is `shortcuts/default.cfg`; it can be edited with any text editor. The shortcut dialog separates shortcut assignment and preset management into bordered sections. **Preset** is an editable combo box: choose an existing preset from the list or type a new name before saving. The dialog can load a preset into the draft, save/overwrite the current draft as a preset, delete a preset after confirmation, and refresh the combo-box list. Loading a preset does not change the active calculator bindings until **Save** is pressed. On a fresh install, `default.cfg` is used when valid. **Restore Defaults**, however, always rebuilds the pristine compiled-in shortcut table, so it still works even if `default.cfg` has been edited, damaged, or deleted. Active bindings continue to be stored in `OpenCalc.cfg`. Duplicate assignments are rejected. Graph editing and native text-selection commands retain their normal behavior.

Preset files use the same simple `shortcut.<action>=key, key` syntax as the active settings, for example `shortcut.clear=C, Escape` and `shortcut.memory_store=Ctrl+M`. Lines beginning with `#` or `;` are comments. Unknown action IDs are ignored for forward compatibility; malformed or conflicting bindings are rejected when the preset is loaded.

Keep the included Cargo.lock when building: it locks the wxDragon support libraries to versions compatible with wxdragon 0.9.17.

### Complete expression parsing

An obscure feature rediscovered in the Windows 95 Calculator is its ability to evaluate complete expressions pasted from the clipboard.

For example, copying:

```text
3 * (4 + 5)
```

and pasting it into Calculator produces:

```text
27
```

This is surprisingly advanced for such an old application!

The pasted expression can contain multiple operations and parentheses, even though the normal calculator interface is designed around entering one operation at a time.

However, our reverse engineering showed that the original implementation was not a true expression parser. It was closer to a **character-to-button-command translator**.

When text was pasted, the program read each character and converted it into the same internal commands used by the calculator buttons. In simplified terms, pasting:

```text
2 * 3
```

was treated roughly like pressing:

```text
[2] [*] [3] [=]
```

This works for many ordinary expressions, but it breaks when the meaning of a character depends on its position in the expression.

The clearest example is a negative number following an operator.

The mathematically correct result of:

```text
2 * -3
```

is:

```text
-6
```

The Windows 95 Calculator instead produced:

```text
-1
```

This happened because the paste feature translated the expression into a sequence resembling ordinary button presses:

```text
[2] [*] [-] [3] [=]
```
After * was pressed, the calculator stored 2 and waited for the second operand. However, in the calculator's button-driven state machine, pressing another binary operator at that point did not make the next number negative. Instead, it replaced the pending operation.

Therefore, the - replaced the earlier *, and the calculator effectively evaluated:
```text
2 - 3
```
which produced:

```text
-1
```

The same underlying bug affected several other expressions:

| Pasted expression | Correct result | Original result |
|---|---:|---:|
| `2 * -3` | `-6` | `-1` |
| `2 / -3` | approximately `-0.6666667` | `-1` |
| `2 - -3` | `5` | `-1` |
| `2 * +3` | `6` | `5` |

The problem was that the original paste routine did not consistently distinguish between:

- binary subtraction, as in `5 - 2`;
- a unary negative sign, as in `-3`;
- a unary sign following another operator, as in `2 * -3`.

It contained special handling for a minus sign at the beginning of an expression and for signs used in exponent notation, but signs appearing after ordinary operators were still passed through the calculator's button-oriented state machine.

Consequently, the `-` in:

```text
2 * -3
```

was not reliably interpreted as “the following number is negative.” It could instead replace or interfere with the pending multiplication operation.

The feature therefore gave the impression of being a full infix-expression parser because expressions such as these worked:

```text
3 * (4 + 5)
(2 + 3) * 4
10 / (2 + 3)
```

But its behavior was actually dependent on whether the pasted character sequence happened to map cleanly onto the calculator's existing button state.

OpenCalc preserves the original paste feature but replaces that command-stream translation with a dedicated parser.

The same policy is used for obsolete capacity limits: OpenCalc keeps the recovered calculator semantics, but does not impose the original 25-level parenthesis ceiling or 13-digit Decimal mantissa-entry ceiling.

The expression is first divided into meaningful tokens:

```text
number
operator
unary sign
function
constant
parenthesis
```

Those tokens are then parsed according to explicit precedence and associativity rules. A minus sign can therefore be interpreted according to its context rather than always being treated like a press of the subtraction button.

The previously broken expressions now behave correctly:

| Expression | OpenCalc result |
|---|---:|
| `2 * -3` | `-6` |
| `2 / -3` | approximately `-0.6666667` |
| `2 - -3` | `5` |
| `2 * +3` | `6` |

The new parser also allows OpenCalc to support syntax that the original implementation did not provide consistently:

```text
3 * (4 + 5)
sqrt(3)
sin(pi / 2)
2**8
(2 + 5)^3
5!
```

Supported features include:

- Dynamically nested parentheses (OpenCalc intentionally does not reproduce the Windows 95 25-level cap);
- Unary positive and negative signs;
- Exponentiation using `^` or `**`;
- Square roots and mathematical functions;
- Trigonometric and logarithmic functions;
- Constants such as `pi`;
- Postfix factorial and percentage operators;
- Scientific notation;
- Binary, octal, decimal, and hexadecimal literals;
- Bitwise operations;
- Case-insensitive function and operator names.

## Disclaimer

OpenCalc is an independent open-source reimplementation. It is not affiliated with, endorsed by, or distributed by Microsoft.
Windows and Windows 95 are trademarks of Microsoft Corporation.