sha256.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <math.h>

static const uint32_t K[] =
{
    0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b,
    0x59f111f1, 0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01,
    0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7,
    0xc19bf174, 0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
    0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da, 0x983e5152,
    0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147,
    0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc,
    0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
    0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819,
    0xd6990624, 0xf40e3585, 0x106aa070, 0x19a4c116, 0x1e376c08,
    0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f,
    0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
    0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
};

static uint8_t *digest(const char *msg)
{
    uint32_t h0 = 0x6a09e667,
            h1 = 0xbb67ae85,
            h2 = 0x3c6ef372,
            h3 = 0xa54ff53a,
            h4 = 0x510e527f,
            h5 = 0x9b05688c,
            h6 = 0x1f83d9ab,
            h7 = 0x5be0cd19;
    const size_t len = strlen(msg),
        byte_len = floor((len + 72) / 64) * 64,
        bit_len = len * 8,
        word_len = byte_len / 4;

    uint8_t *m = malloc(byte_len * sizeof(size_t));

    for (int i = 0; i < len; ++i)
        m[i] = msg[i];
    for (int i = len; i < byte_len; ++i)
        m[i] = 0;
}