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use murmur3_32 hash 

it is more efficient than the previously used djb hash
cute-signatures
Timo Teräs 2015-06-11 16:54:13 +03:00
parent 4fab9290b6
commit ed94d8ffba
1 changed files with 46 additions and 7 deletions
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53
src/blob.c
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@ -200,15 +200,54 @@ apk_blob_t apk_blob_pushed(apk_blob_t buffer, apk_blob_t left)
return APK_BLOB_PTR_LEN(buffer.ptr, left.ptr - buffer.ptr);
}
static uint32_t murmur3_32(const char *key, uint32_t len, uint32_t seed)
{
static const uint32_t c1 = 0xcc9e2d51;
static const uint32_t c2 = 0x1b873593;
static const uint32_t r1 = 15;
static const uint32_t r2 = 13;
static const uint32_t m = 5;
static const uint32_t n = 0xe6546b64;
uint32_t hash = seed;
const int nblocks = len / 4;
const uint32_t *blocks = (const uint32_t *) key;
int i;
for (i = 0; i < nblocks; i++) {
uint32_t k = blocks[i];
k *= c1;
k = (k << r1) | (k >> (32 - r1));
k *= c2;
hash ^= k;
hash = ((hash << r2) | (hash >> (32 - r2))) * m + n;
}
const uint8_t *tail = (const uint8_t *) (key + nblocks * 4);
uint32_t k1 = 0;
switch (len & 3) {
case 3:
k1 ^= tail[2] << 16;
case 2:
k1 ^= tail[1] << 8;
case 1:
k1 ^= tail[0];
k1 *= c1;
k1 = (k1 << r1) | (k1 >> (32 - r1));
k1 *= c2;
hash ^= k1;
}
hash ^= len;
hash ^= (hash >> 16);
hash *= 0x85ebca6b;
hash ^= (hash >> 13);
hash *= 0xc2b2ae35;
hash ^= (hash >> 16);
return hash;
}
unsigned long apk_blob_hash_seed(apk_blob_t blob, unsigned long seed)
{
unsigned long hash = seed;
int i;
for (i = 0; i < blob.len; i++)
hash = hash * 33 + blob.ptr[i];
return hash;
return murmur3_32(blob.ptr, blob.len, seed);
}
unsigned long apk_blob_hash(apk_blob_t blob)