Making portable my unportable transputer C compiler

A found floppy contained a 1998 C compiler for the transputer that had been ported to DJGPP/G++ but would not compile on a modern 64-bit Mac M1 because the original code relied on 32-bit assumptions: pointers and integers were used interchangeably, FILE was treated as int, there were no function prototypes, and Small-C heritage stored structures and types in a byte pool with 32-bit words. The goal was to change as little as possible so the compiler would build on a 64-bit host while still being able to compile itself for the transputer using only features implemented by the compiler. Key portability problems included saving 32-bit pointers in integer arrays, hard-coded offsets for symbol table entries, and expression nodes that mixed pointer and integer uses.

The porting approach replaced fragile integer arrays with proper structs (including FILE fields and K&R-style prototypes), rewrote include-state handling to store pointers in a struct array, and converted many int-based type and node representations to typed structs or indices. The author incrementally fixed dozens of pointer/int errors (reporting reductions from dozens to 25, then 8, then 5, and finally zero), added small node fields instead of complex unions, and adjusted symbol tables to a struct-based layout. After resolving runtime issues (undefined NULL and use of fputs/stdout), the compiler assembled and produced a smaller, working cc2 executable; emitted assembler matched previous output and the compiler successfully ran in the transputer operating system.