gecko-dev/netwerk/cache2/CacheHashUtils.cpp

88 строки
2.5 KiB
C++

/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "CacheHashUtils.h"
#include "plstr.h"
namespace mozilla {
namespace net {
/**
* CacheHashUtils::Hash(const char * key, uint32_t initval)
*
* See http://burtleburtle.net/bob/hash/evahash.html for more information
* about this hash function.
*
* This algorithm is used to check the data integrity.
*/
static inline void hashmix(uint32_t& a, uint32_t& b, uint32_t& c)
{
a -= b; a -= c; a ^= (c>>13);
b -= c; b -= a; b ^= (a<<8);
c -= a; c -= b; c ^= (b>>13);
a -= b; a -= c; a ^= (c>>12);
b -= c; b -= a; b ^= (a<<16);
c -= a; c -= b; c ^= (b>>5);
a -= b; a -= c; a ^= (c>>3);
b -= c; b -= a; b ^= (a<<10);
c -= a; c -= b; c ^= (b>>15);
}
CacheHashUtils::Hash32_t
CacheHashUtils::Hash(const char *aData, uint32_t aSize, uint32_t aInitval)
{
const uint8_t *k = reinterpret_cast<const uint8_t*>(aData);
uint32_t a, b, c, len/*, length*/;
// length = PL_strlen(key);
/* Set up the internal state */
len = aSize;
a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
c = aInitval; /* variable initialization of internal state */
/*---------------------------------------- handle most of the key */
while (len >= 12)
{
a += k[0] + (uint32_t(k[1])<<8) + (uint32_t(k[2])<<16) + (uint32_t(k[3])<<24);
b += k[4] + (uint32_t(k[5])<<8) + (uint32_t(k[6])<<16) + (uint32_t(k[7])<<24);
c += k[8] + (uint32_t(k[9])<<8) + (uint32_t(k[10])<<16) + (uint32_t(k[11])<<24);
hashmix(a, b, c);
k += 12; len -= 12;
}
/*------------------------------------- handle the last 11 bytes */
c += aSize;
switch(len) { /* all the case statements fall through */
case 11: c += (uint32_t(k[10])<<24);
case 10: c += (uint32_t(k[9])<<16);
case 9 : c += (uint32_t(k[8])<<8);
/* the low-order byte of c is reserved for the length */
case 8 : b += (uint32_t(k[7])<<24);
case 7 : b += (uint32_t(k[6])<<16);
case 6 : b += (uint32_t(k[5])<<8);
case 5 : b += k[4];
case 4 : a += (uint32_t(k[3])<<24);
case 3 : a += (uint32_t(k[2])<<16);
case 2 : a += (uint32_t(k[1])<<8);
case 1 : a += k[0];
/* case 0: nothing left to add */
}
hashmix(a, b, c);
return c;
}
CacheHashUtils::Hash16_t
CacheHashUtils::Hash16(const char *aData, uint32_t aSize, uint32_t aInitval)
{
Hash32_t hash = Hash(aData, aSize, aInitval);
return (hash & 0xFFFF);
}
} // net
} // mozilla