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// File: lzham_checksum.cpp
#include "lzham_core.h"
#include "lzham_checksum.h"
namespace lzham
{
// Originally from the public domain stb.h header.
uint adler32(const void* pBuf, size_t buflen, uint adler32)
{
if (!pBuf)
return cInitAdler32;
const uint8* buffer = static_cast<const uint8*>(pBuf);
const unsigned long ADLER_MOD = 65521;
unsigned long s1 = adler32 & 0xffff, s2 = adler32 >> 16;
size_t blocklen;
unsigned long i;
blocklen = buflen % 5552;
while (buflen)
{
for (i=0; i + 7 < blocklen; i += 8)
{
s1 += buffer[0], s2 += s1;
s1 += buffer[1], s2 += s1;
s1 += buffer[2], s2 += s1;
s1 += buffer[3], s2 += s1;
s1 += buffer[4], s2 += s1;
s1 += buffer[5], s2 += s1;
s1 += buffer[6], s2 += s1;
s1 += buffer[7], s2 += s1;
buffer += 8;
}
for (; i < blocklen; ++i)
s1 += *buffer++, s2 += s1;
s1 %= ADLER_MOD, s2 %= ADLER_MOD;
buflen -= blocklen;
blocklen = 5552;
}
return static_cast<uint>((s2 << 16) + s1);
}
// Karl Malbrain's compact CRC-32, with pre and post conditioning.
// See "A compact CCITT crc16 and crc32 C implementation that balances processor cache usage against speed":
// http://www.geocities.com/malbrain/
static const lzham_uint32 s_crc32[16] =
{
0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac, 0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c, 0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c
};
uint crc32(uint crc, const lzham_uint8 *ptr, size_t buf_len)
{
if (!ptr)
return cInitCRC32;
crc = ~crc;
while (buf_len--)
{
lzham_uint8 b = *ptr++;
crc = (crc >> 4) ^ s_crc32[(crc & 0xF) ^ (b & 0xF)];
crc = (crc >> 4) ^ s_crc32[(crc & 0xF) ^ (b >> 4)];
}
return ~crc;
}
} // namespace lzham
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