From 68d9da9746d235e2d9a7d0ba61310c533b355847 Mon Sep 17 00:00:00 2001
From: nsfisis <nsfisis@gmail.com>
Date: Wed, 7 May 2025 09:13:49 +0900
Subject: copy files from P4Dcc

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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, it deletegates to gcc as-is.
+
+This project was started to prove 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):
+
+* Simplified 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
+* Minimal syntax sugar
+    * ~~No increment/decrement operators~~
+        * Partially implemented after self-hosting
+    * ~~No compound assignment operators~~
+        * Implemented after self-hosting
+    * ~~No `while`~~
+        * Implemented after self-hosting
+    * No `switch`
+* 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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