eisenstein-c

The same exact hex arithmetic as the Rust crate, compiled to ~1KB of .text.

No runtime. No heap. No operating system. Just stdint.h and 600 lines of C that do exactly what the Rust version does — Eisenstein integer arithmetic with integer arithmetic. This is the port you use when there's no allocator, no FPU, and you need to know exactly how many cycles every operation takes.

Quick Start

#include "eisenstein.h"

E12 z = eisenstein_new(-5, 3);
int32_t n = eisenstein_norm(z);  // 49, exact integer
E12 rotated = eisenstein_rotate_60(z);

What's Included

• E12 — two int32_ts, same representation as the Rust crate
• Norm — a² - ab + b², no sqrt, no float, no libm
• 60° rotation — (-b, a - b), two subtractions and a negation
• D₆ symmetry — all six rotations
• Addition, multiplication, negation, conjugate

Build

cc -O2 -c eisenstein.c -o eisenstein.o

Single translation unit. No linker dependencies beyond libc (and you can drop that too). 18 tests, all pass.

Why C?

The Rust crate is the reference. This C port exists for environments the Rust compiler doesn't target:

• ARM Cortex-M4, RV32, and other microcontrollers
• Bootloaders and firmware
• Kernels and hypervisors
• Safety-critical certification stacks that require C source

License

MIT OR Apache-2.0