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

typedef uint8_t byte;

typedef byte hash[ 32 ];

static uint32_t ror(uint32_t x, int n) { return (x >> n) | (x << (32 - n)); }

static uint32_t ch(uint32_t x, uint32_t y, uint32_t z) { return (x & y) ^ (~x & z); }

static uint32_t maj(uint32_t x, uint32_t y, uint32_t z) { return (x & y) ^ (x & z) ^ (y & z); }

static uint32_t sigma0(uint32_t x) { return ror(x, 2) ^ ror(x, 13) ^ ror(x, 22); }

static uint32_t sigma1(uint32_t x) { return ror(x, 6) ^ ror(x, 11) ^ ror(x, 25); }

static uint32_t gamma0(uint32_t x) { return ror(x, 7) ^ ror(x, 18) ^ (x >> 3); }

static uint32_t gamma1(uint32_t x) { return ror(x, 17) ^ ror(x, 19) ^ (x >> 10); }

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 void sha256_compress(uint32_t state[ 8 ], const byte block[ 64 ]) {
    uint32_t w[ 64 ];
    int      i;
    for (i = 0; i < 16; i++) {
        w[ i ] = (block[ i * 4 ] << 24) | (block[ i * 4 + 1 ] << 16) | (block[ i * 4 + 2 ] << 8)
                 | block[ i * 4 + 3 ];
    }
    for (i = 16; i < 64; i++) {
        w[ i ] = gamma1(w[ i - 2 ]) + w[ i - 7 ] + gamma0(w[ i - 15 ]) + w[ i - 16 ];
    }
    uint32_t a = state[ 0 ], b = state[ 1 ], c = state[ 2 ], d = state[ 3 ], e = state[ 4 ],
             f = state[ 5 ], g = state[ 6 ], h = state[ 7 ];
    for (i = 0; i < 64; i++) {
        uint32_t t1 = h + sigma1(e) + ch(e, f, g) + K[ i ] + w[ i ];
        uint32_t t2 = sigma0(a) + maj(a, b, c);
        h           = g;
        g           = f;
        f           = e;
        e           = d + t1;
        d           = c;
        c           = b;
        b           = a;
        a           = t1 + t2;
    }
    state[ 0 ] += a;
    state[ 1 ] += b;
    state[ 2 ] += c;
    state[ 3 ] += d;
    state[ 4 ] += e;
    state[ 5 ] += f;
    state[ 6 ] += g;
    state[ 7 ] += h;
}

struct sha256 {
    hash hash;
} sha256_hash(const byte *in, size_t in_len) {
    struct sha256 out;

    uint32_t state[ 8 ] = { 0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
                            0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19 };
    size_t   off        = 0;
    for (; off + 64 <= in_len; off += 64) { sha256_compress(state, in + off); }
    byte pad[ 128 ];
    memset(pad, 0, sizeof(pad));
    size_t rem = in_len - off;
    memcpy(pad, in + off, rem);
    pad[ rem ]            = 0x80;
    int    use_two_blocks = (rem >= 56);
    size_t pad_len        = 64 + 64 * use_two_blocks;
    size_t pos            = rem + 1;
    while (pos < pad_len - 8) { pad[ pos++ ] = 0; }
    uint64_t bit_len   = in_len * 8;
    pad[ pad_len - 1 ] = bit_len & 0xff;
    pad[ pad_len - 2 ] = (bit_len >> 8) & 0xff;
    pad[ pad_len - 3 ] = (bit_len >> 16) & 0xff;
    pad[ pad_len - 4 ] = (bit_len >> 24) & 0xff;
    pad[ pad_len - 5 ] = (bit_len >> 32) & 0xff;
    pad[ pad_len - 6 ] = (bit_len >> 40) & 0xff;
    pad[ pad_len - 7 ] = (bit_len >> 48) & 0xff;
    pad[ pad_len - 8 ] = (bit_len >> 56) & 0xff;
    sha256_compress(state, pad);
    if (use_two_blocks) { sha256_compress(state, pad + 64); }
    for (int i = 0; i < 8; i++) {
        out.hash[ 4 * i ]     = (state[ i ] >> 24) & 0xff;
        out.hash[ 4 * i + 1 ] = (state[ i ] >> 16) & 0xff;
        out.hash[ 4 * i + 2 ] = (state[ i ] >> 8) & 0xff;
        out.hash[ 4 * i + 3 ] = state[ i ] & 0xff;
    }

    return out;
}