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# P4Dcc
P4Dcc is a tiny, but self-hosted C compiler. It takes C source code and compiles it to assembly language. For assembling and linking, I use gcc as-is.
This project was started to test the hypothesis: "Could a self-hostable C compiler be built in four days, if the feature set is carefully limited?" - "P4D" stands for the ISO 8601 notation meaning "four days." However, I actually completed the project by the morning of the third day.
The code is written following the instructions at https://www.sigbus.info/compilerbook, and several key design decisions were inspired by the book.
## Dependencies
* gcc
* [just](https://github.com/casey/just), a general-purpose task runner
## Build
```
$ just build
```
## Test
```
$ just test
$ just test-all # test all things, including binary equiality between generations
```
## Design
To meet the four-day goal, many design decisions were made to reduce complexity (ideas directly taken from https://www.sigbus.info/compilerbook are not listed):
* Simplify declaration syntax
* No support for `typedef`
* Structs always begin with `struct` keyword
* No support for array types
* No stack-allocated arrays
* All arrays are heap-allocated and accessed via pointers
* No support for function types
* Type information always precede the variable name
* Most syntax sugar is not implemented
* No increment/decrement operators
* ~~No compound assignment operators~~
* Implemented after self-hosting
* ~~No `while`~~
* Implemented after self-hosting
* Limited preprocessor
* Supports only simple `#define` that replaces identifiers with single integer or identifier
* No global variables
* Including `stdin`, `stdout`, and `stderr`
* Only function/struct definitions/declarations are allowed at the top level
* No variable shadowing
* All variables are function-scoped
## License
See [LICENSE](./LICENSE).
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