File content as of revision 0:772b6de3a841:

// Author: Remco Bloemen
// Based on:
//   http://en.wikipedia.org/wiki/SHA-2
//   http://www.iwar.org.uk/comsec/resources/cipher/sha256-384-512.pdf

#include "SHA256.h"

inline unsigned int byte_swap(unsigned int x)
{
    // unsigned int result;
    // asm("REV %0, %1" : "=r"(result) : "r"(x));
    // return result
    return __rev(x);
}

inline unsigned int rotate_right(unsigned int x, int shift)
{
    return (x >> shift) | (x << (32 - shift));
}

const unsigned int 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
};

inline unsigned int s0(unsigned int x) {
    return rotate_right(x, 7) ^ rotate_right(x, 18) ^ (x >> 3);
}

inline unsigned int s1(unsigned int x) {
    return rotate_right(x, 17) ^ rotate_right(x, 19) ^ (x >> 10);
}

inline unsigned int s2(unsigned int x) {
    return rotate_right(x, 2) ^ rotate_right(x, 13) ^ rotate_right(x, 22);
}

inline unsigned int s3(unsigned int x) {
    return rotate_right(x, 6) ^ rotate_right(x, 11) ^ rotate_right(x, 25);
}

void SHA256::reset()
{
    hash[0] = 0x6A09E667;
    hash[1] = 0xBB67AE85;
    hash[2] = 0x3C6EF372;
    hash[3] = 0xA54FF53A;
    hash[4] = 0x510E527F;
    hash[5] = 0x9B05688C;
    hash[6] = 0x1F83D9AB;
    hash[7] = 0x5BE0CD19;
    length = 0;
}

void SHA256::append(const char* data, int size)
{
    const char* end = data + size;
    char* buffer = reinterpret_cast<char*>(w);
    
    // TODO: operate in words
    
    int index = length % 64;
    while(data != end) {
        int word_index = index / 4;
        int byte_index = index % 4;
        buffer[4 * word_index + 3 - byte_index] = *data;
        ++index;
        ++data;
        if(index == 64) {
            process_chunk();
            index = 0;
        }
    }
    length += size;
}

void SHA256::finalize()
{
    int trailing = length % 64;
    
    // Append the bit '1' to the message
    int last_block = trailing / 4;
    unsigned int bit_in_block = 0x80 << (24 - (trailing % 4) * 8); 
    w[last_block] |= bit_in_block;
    w[last_block] &= ~(bit_in_block - 1);
    
    // Set all other bits to zero
    for(int i = last_block + 1; i < 15; ++i)
        w[i] = 0;
    
    // Make room for the length if necessary
    if(trailing >= 56) {
        process_chunk();
        for(int i = 0; i <= last_block; ++i)
            w[i] = 0;
    }
    
    // Append the length in bits
    w[14] = length >> (32 - 3);
    w[15] = length << 3;
    process_chunk();
    
    // Convert the result to big endian
    for(int i = 0; i < 8; ++i)
       hash[i] = byte_swap(hash[i]);
}

// Process a 512 bit chunk stored in w[1...15]
void SHA256::process_chunk()
{
    // Extend the chunk to 64 x 32 bit
    for(int i = 16; i < 64; ++i)
        w[i] = w[i - 16] + s0(w[i - 15]) + w[i - 7] + s1(w[i - 2]);
    
    // Initialize using current hash
    unsigned int a = hash[0];
    unsigned int b = hash[1];
    unsigned int c = hash[2];
    unsigned int d = hash[3];
    unsigned int e = hash[4];
    unsigned int f = hash[5];
    unsigned int g = hash[6];
    unsigned int h = hash[7];
    
    // Main loop
    for(int i = 0; i < 64; ++i) {
        unsigned int maj = (a & b) ^ (a & c) ^ (b & c);
        unsigned int ch = (e & f) ^ ((~e) & g);
        unsigned int t1 = h + s3(e) + ch + k[i] + w[i];
        unsigned int t2 = maj + s2(a);
        h = g;
        g = f;
        f = e;
        e = d + t1;
        d = c;
        c = b;
        b = a;
        a = t1 + t2;
    }
    
    // Update hash
    hash[0] += a;
    hash[1] += b;
    hash[2] += c;
    hash[3] += d;
    hash[4] += e;
    hash[5] += f;
    hash[6] += g;
    hash[7] += h; 
}