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Merge pull request #1304 from FioraAeterna/fasterhash 

Hash: unroll CRC loop, since CRC32 typically has nontrivial latency
This commit is contained in:
comex 2014-10-17 20:24:47 -04:00
parent dfd719124f 15a4bccb73
commit 2684c75c6e
1 changed files with 15 additions and 5 deletions
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20
Source/Core/Common/Hash.cpp
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@ -230,21 +230,31 @@ u64 GetMurmurHash3(const u8 *src, int len, u32 samples)
u64 GetCRC32(const u8 *src, int len, u32 samples) u64 GetCRC32(const u8 *src, int len, u32 samples)
{ {
#if _M_SSE >= 0x402 #if _M_SSE >= 0x402
u64 h = len; u64 h[4] = { len, 0, 0, 0 };
u32 Step = (len / 8); u32 Step = (len / 8);
const u64 *data = (const u64 *)src; const u64 *data = (const u64 *)src;
const u64 *end = data + Step; const u64 *end = data + Step;
if (samples == 0) samples = std::max(Step, 1u); if (samples == 0) samples = std::max(Step, 1u);
Step = Step / samples; Step = Step / samples;
if (Step < 1) Step = 1; if (Step < 1) Step = 1;
while (data < end) while (data < end - Step * 3)
{ {
h = _mm_crc32_u64(h, data[0]); h[0] = _mm_crc32_u64(h[0], data[Step * 0]);
data += Step; h[1] = _mm_crc32_u64(h[1], data[Step * 1]);
h[2] = _mm_crc32_u64(h[2], data[Step * 2]);
h[3] = _mm_crc32_u64(h[3], data[Step * 3]);
data += Step * 4;
} }
if (data < end - Step * 0)
h[0] = _mm_crc32_u64(h[0], data[Step * 0]);
if (data < end - Step * 1)
h[1] = _mm_crc32_u64(h[1], data[Step * 1]);
if (data < end - Step * 2)
h[2] = _mm_crc32_u64(h[2], data[Step * 2]);
const u8 *data2 = (const u8*)end; const u8 *data2 = (const u8*)end;
return _mm_crc32_u64(h, u64(data2[0])); // FIXME: is there a better way to combine these partial hashes?
return _mm_crc32_u64(h[0] + h[1] + h[2] + h[3], u64(data2[0]));
#else #else
return 0; return 0;
#endif #endif