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

#include "sha256.h"


// DBL_INT_ADD treats two unsigned ints a and b as one 64-bit integer and adds c to it
#define DBL_INT_ADD(a,b,c) if (a > 0xffffffff - (c)) ++b; a += c;
#define ROTLEFT(a,b) (((a) << (b)) | ((a) >> (32-(b))))
#define ROTRIGHT(a,b) (((a) >> (b)) | ((a) << (32-(b))))

#define CH(x,y,z) (((x) & (y)) ^ (~(x) & (z)))
#define MAJ(x,y,z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
#define EP0(x) (ROTRIGHT(x,2) ^ ROTRIGHT(x,13) ^ ROTRIGHT(x,22))
#define EP1(x) (ROTRIGHT(x,6) ^ ROTRIGHT(x,11) ^ ROTRIGHT(x,25))
#define SIG0(x) (ROTRIGHT(x,7) ^ ROTRIGHT(x,18) ^ ((x) >> 3))
#define SIG1(x) (ROTRIGHT(x,17) ^ ROTRIGHT(x,19) ^ ((x) >> 10))


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
};


void
sha256_transform( SHA256_CTX * ctx, uint8_t data[] )
{
    uint32_t a, b, c, d, e, f, g, h, i, j, t1, t2, m[64];

    for ( i = 0, j = 0; i < 16; ++i, j += 4 )
        m[i] =
            ( data[j] << 24 ) | ( data[j + 1] << 16 ) | ( data[j + 2] << 8 ) |
            ( data[j + 3] );
    for ( ; i < 64; ++i )
        m[i] = SIG1( m[i - 2] ) + m[i - 7] + SIG0( m[i - 15] ) + m[i - 16];

    a = ctx->state[0];
    b = ctx->state[1];
    c = ctx->state[2];
    d = ctx->state[3];
    e = ctx->state[4];
    f = ctx->state[5];
    g = ctx->state[6];
    h = ctx->state[7];

    for ( i = 0; i < 64; ++i )
    {
        t1 = h + EP1( e ) + CH( e, f, g ) + k[i] + m[i];
        t2 = EP0( a ) + MAJ( a, b, c );
        h = g;
        g = f;
        f = e;
        e = d + t1;
        d = c;
        c = b;
        b = a;
        a = t1 + t2;
    }

    ctx->state[0] += a;
    ctx->state[1] += b;
    ctx->state[2] += c;
    ctx->state[3] += d;
    ctx->state[4] += e;
    ctx->state[5] += f;
    ctx->state[6] += g;
    ctx->state[7] += h;
}

void
sha256_init( SHA256_CTX * ctx )
{
    ctx->datalen = 0;
    ctx->bitlen[0] = 0;
    ctx->bitlen[1] = 0;
    ctx->state[0] = 0x6a09e667;
    ctx->state[1] = 0xbb67ae85;
    ctx->state[2] = 0x3c6ef372;
    ctx->state[3] = 0xa54ff53a;
    ctx->state[4] = 0x510e527f;
    ctx->state[5] = 0x9b05688c;
    ctx->state[6] = 0x1f83d9ab;
    ctx->state[7] = 0x5be0cd19;
}

void
sha256_update( SHA256_CTX * ctx, char data[], uint32_t len )
{
    uint32_t i;

    for ( i = 0; i < len; ++i )
    {
        ctx->data[ctx->datalen] = data[i];
        ctx->datalen++;
        if ( ctx->datalen == 64 )
        {
            sha256_transform( ctx, ctx->data );
            DBL_INT_ADD( ctx->bitlen[0], ctx->bitlen[1], 512 );
            ctx->datalen = 0;
        }
    }
}

void
sha256_final( SHA256_CTX * ctx, uint8_t hash[] )
{
    uint32_t i;

    i = ctx->datalen;

    // Pad whatever data is left in the buffer. 
    if ( ctx->datalen < 56 )
    {
        ctx->data[i++] = 0x80;
        while ( i < 56 )
            ctx->data[i++] = 0x00;
    }
    else
    {
        ctx->data[i++] = 0x80;
        while ( i < 64 )
            ctx->data[i++] = 0x00;
        sha256_transform( ctx, ctx->data );
        memset( ctx->data, 0, 56 );
    }

    // Append to the padding the total message's length in bits and transform. 
    DBL_INT_ADD( ctx->bitlen[0], ctx->bitlen[1], ctx->datalen * 8 );
    ctx->data[63] = ctx->bitlen[0];
    ctx->data[62] = ctx->bitlen[0] >> 8;
    ctx->data[61] = ctx->bitlen[0] >> 16;
    ctx->data[60] = ctx->bitlen[0] >> 24;
    ctx->data[59] = ctx->bitlen[1];
    ctx->data[58] = ctx->bitlen[1] >> 8;
    ctx->data[57] = ctx->bitlen[1] >> 16;
    ctx->data[56] = ctx->bitlen[1] >> 24;
    sha256_transform( ctx, ctx->data );

    // Since this implementation uses little endian byte ordering and SHA uses big endian,
    // reverse all the bytes when copying the final state to the output hash. 
    for ( i = 0; i < 4; ++i )
    {
        hash[i] = ( ctx->state[0] >> ( 24 - i * 8 ) ) & 0x000000ff;
        hash[i + 4] = ( ctx->state[1] >> ( 24 - i * 8 ) ) & 0x000000ff;
        hash[i + 8] = ( ctx->state[2] >> ( 24 - i * 8 ) ) & 0x000000ff;
        hash[i + 12] = ( ctx->state[3] >> ( 24 - i * 8 ) ) & 0x000000ff;
        hash[i + 16] = ( ctx->state[4] >> ( 24 - i * 8 ) ) & 0x000000ff;
        hash[i + 20] = ( ctx->state[5] >> ( 24 - i * 8 ) ) & 0x000000ff;
        hash[i + 24] = ( ctx->state[6] >> ( 24 - i * 8 ) ) & 0x000000ff;
        hash[i + 28] = ( ctx->state[7] >> ( 24 - i * 8 ) ) & 0x000000ff;
    }
}