/*
   C implementation by John Ryland
   Based on psuedo code algorithm on wikipedia
   Copyright (c) 2013
 */

#include <assert.h>
#include <endian.h>
#include <string.h>
#include "SHA256.h"


// Initialize variables
// (first 32 bits of the fractional parts of the square roots of the first 8 primes 2..19):
static const uint32_t h[8] =
{
  0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a, 0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19
};


// Initialize table of round constants
// (first 32 bits of the fractional parts of the cube roots of the first 64 primes 2..311):
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
};


void sha256(const uint8_t* message, uint64_t length, uint32_t hash[8])
{
  // Initialize hash value
  memcpy(hash, h, 8*sizeof(uint32_t));

  // append the bit '1' to the message
  // append k bits '0', where k is the minimum number >= 0 such that the resulting message
  //    length (in bits) is 448 (modulo 512).
  uint8_t msg[length + 65];
  memcpy(msg, message, length);
  msg[length] = 0x80;

  uint64_t bitLength = (length+1) * 8;
  for (int i = 1; i < 64; i++)
    msg[length+i] = 0x00;
  if ( (bitLength % 512) > 448 ) {
    bitLength = (512 - (bitLength % 512)) + 448;
  } else {
    bitLength += 448 - (bitLength % 512);
  }
  assert((bitLength % 512) == 448);

  // append length of message (before pre-processing), in bits, as 64-bit big-endian integer
  length *= 8;
  *((uint64_t*)(msg + (bitLength/8))) = htobe64(length);
  bitLength += 64;

  // Process the message in successive 512-bit chunks:
  for (uint64_t bit = 0ULL; bit < bitLength; bit += 512)
  {
    uint32_t chunk[64];
    for (int i = 0; i < 16; i++)
    {
      // break chunk into sixteen 32-bit big-endian words w[0..15]
      chunk[i] = be32toh(((uint32_t*)&msg[bit/8])[i]);
    }

    // Extend the sixteen 32-bit words into sixty-four 32-bit words:
    for (int i = 16; i < 64; i++)
    {
      // we can do rotate right in C using shift right if we duplicate the bits
      uint32_t s0 = chunk[i - 15];
      uint32_t s1 = chunk[i - 2];
      uint64_t v = (uint64_t(s0) << 32) | s0;
      s0 = (v >> 7) ^ (v >> 18) ^ (s0 >> 3);
      v = (uint64_t(s1) << 32) | s1;
      s1 = (v >> 17) ^ (v >> 19) ^ (s1 >> 10);
      chunk[i] = chunk[i - 16] + s0 + chunk[i - 7] + s1;
    }

    uint32_t x[8];
    memcpy(x, hash, 8*sizeof(uint32_t));

    // Main loop:
    for (int i = 0; i < 64; i++)
    {
      uint64_t v = (uint64_t(x[4]) << 32) | x[4];
      uint32_t temp = x[7] + 
        ((v >> 6) ^ (v >> 11) ^ (v >> 25)) +
        ((x[4] & x[5]) ^ (~x[4] & x[6])) +
        k[i] + chunk[i];
      x[3] += temp;
      for (int j = 7; j; --j)
        x[j] = x[j - 1];
      v = (uint64_t(x[0]) << 32) | x[0];
      temp += ((v >> 2) ^ (v >> 13) ^ (v >> 22)) + 
        ((x[0] & (x[2] ^ x[3])) ^ (x[2] & x[3]));
      x[0] = temp;
    }

    // Add this chunk's hash to result so far:
    for (int i = 0; i < 8; ++i)
      hash[i] += x[i];
  }

  // the final hash value (big-endian) is in hash
}