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Cleanup (safe, it was checked) subscript[0] in MurmurHash3 (and cleanup MurmurHash3 to be more clear).

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This commit is contained in:
Jeremy Rubin 2017-02-19 13:11:44 -05:00
parent 96f2119e6c
commit 6896dbf169
1 changed files with 20 additions and 23 deletions
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43
src/hash.cpp
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@ -17,36 +17,34 @@ unsigned int MurmurHash3(unsigned int nHashSeed, const std::vector<unsigned char
{
// The following is MurmurHash3 (x86_32), see http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
uint32_t h1 = nHashSeed;
if (vDataToHash.size() > 0)
{
const uint32_t c1 = 0xcc9e2d51;
const uint32_t c2 = 0x1b873593;
const uint32_t c1 = 0xcc9e2d51;
const uint32_t c2 = 0x1b873593;
const int nblocks = vDataToHash.size() / 4;
const int nblocks = vDataToHash.size() / 4;
//----------
// body
const uint8_t* blocks = &vDataToHash[0] + nblocks * 4;
//----------
// body
const uint8_t* blocks = vDataToHash.data();
for (int i = -nblocks; i; i++) {
uint32_t k1 = ReadLE32(blocks + i*4);
for (int i = 0; i < nblocks; ++i) {
uint32_t k1 = ReadLE32(blocks + i*4);
k1 *= c1;
k1 = ROTL32(k1, 15);
k1 *= c2;
k1 *= c1;
k1 = ROTL32(k1, 15);
k1 *= c2;
h1 ^= k1;
h1 = ROTL32(h1, 13);
h1 = h1 * 5 + 0xe6546b64;
}
h1 ^= k1;
h1 = ROTL32(h1, 13);
h1 = h1 * 5 + 0xe6546b64;
}
//----------
// tail
const uint8_t* tail = (const uint8_t*)(&vDataToHash[0] + nblocks * 4);
//----------
// tail
const uint8_t* tail = vDataToHash.data() + nblocks * 4;
uint32_t k1 = 0;
uint32_t k1 = 0;
switch (vDataToHash.size() & 3) {
switch (vDataToHash.size() & 3) {
case 3:
k1 ^= tail[2] << 16;
case 2:
@ -57,7 +55,6 @@ unsigned int MurmurHash3(unsigned int nHashSeed, const std::vector<unsigned char
k1 = ROTL32(k1, 15);
k1 *= c2;
h1 ^= k1;
}
}
//----------