#include "sha256.h"
#include <stdint.h>
#include <string.h>

static const uint32_t K[64] = {
    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 uint32_t rotate(uint32_t x, unsigned n) { return x >> n | x << (32 - n); }

/* One 64-byte block into the state. */
static void block(uint32_t h[8], const unsigned char *p) {
    uint32_t w[64];
    for (unsigned i = 0; i < 16; ++i) w[i] = (uint32_t)p[4 * i] << 24 | (uint32_t)p[4 * i + 1] << 16 | (uint32_t)p[4 * i + 2] << 8 | p[4 * i + 3];
    for (unsigned i = 16; i < 64; ++i) {
        uint32_t s0 = rotate(w[i - 15], 7) ^ rotate(w[i - 15], 18) ^ w[i - 15] >> 3;
        uint32_t s1 = rotate(w[i - 2], 17) ^ rotate(w[i - 2], 19) ^ w[i - 2] >> 10;
        w[i] = w[i - 16] + s0 + w[i - 7] + s1;
    }
    uint32_t a = h[0], b = h[1], c = h[2], d = h[3], e = h[4], f = h[5], g = h[6], k = h[7];
    for (unsigned i = 0; i < 64; ++i) {
        uint32_t t1 = k + (rotate(e, 6) ^ rotate(e, 11) ^ rotate(e, 25)) + ((e & f) ^ (~e & g)) + K[i] + w[i];
        uint32_t t2 = (rotate(a, 2) ^ rotate(a, 13) ^ rotate(a, 22)) + ((a & b) ^ (a & c) ^ (b & c));
        k = g, g = f, f = e, e = d + t1, d = c, c = b, b = a, a = t1 + t2;
    }
    h[0] += a, h[1] += b, h[2] += c, h[3] += d, h[4] += e, h[5] += f, h[6] += g, h[7] += k;
}

void pure_sha256(const void *data, size_t size, unsigned char out[32]) {
    uint32_t h[8] = {0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19};
    const unsigned char *p = data;
    size_t whole = size / 64 * 64;
    for (size_t at = 0; at < whole; at += 64) block(h, p + at);
    /* The rest, a 1 bit, zeros, and the length in bits (one block more when it does not fit). */
    unsigned char last[128] = {0};
    size_t rest = size - whole, blocks = rest < 56 ? 1 : 2;
    if (rest) memcpy(last, p + whole, rest);
    last[rest] = 0x80;
    uint64_t bits = (uint64_t)size * 8;
    for (unsigned i = 0; i < 8; ++i) last[blocks * 64 - 1 - i] = (unsigned char)(bits >> (8 * i));
    for (size_t at = 0; at < blocks * 64; at += 64) block(h, last + at);
    for (unsigned i = 0; i < 8; ++i)
        out[4 * i] = (unsigned char)(h[i] >> 24), out[4 * i + 1] = (unsigned char)(h[i] >> 16),
        out[4 * i + 2] = (unsigned char)(h[i] >> 8), out[4 * i + 3] = (unsigned char)h[i];
}