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SuperFastHash.cpp
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123 lines (107 loc) · 2.91 KB
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#include "SuperFastHash.h"
#include <assert.h>
#include <stdlib.h>
#include "CommonTypeDefines.h"
#if !defined(_WIN32)
#include <stdint.h>
#endif
#undef get16bits
#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
|| defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
#define get16bits(d) (*((const __u16 *) (d)))
#endif
#if !defined (get16bits)
#define get16bits(d) ((((__u32)(((const uint8_t *)(d))[1])) << 8)\
+(__u32)(((const uint8_t *)(d))[0]) )
#endif
static const int INCREMENTAL_READ_BLOCK=65536;
unsigned int SuperFastHash (const char * data, int length)
{
// All this is necessary or the hash does not match SuperFastHashIncremental
int bytesRemaining=length;
unsigned int lastHash = length;
int offset=0;
while (bytesRemaining>=INCREMENTAL_READ_BLOCK)
{
lastHash=SuperFastHashIncremental (data+offset, INCREMENTAL_READ_BLOCK, lastHash );
bytesRemaining-=INCREMENTAL_READ_BLOCK;
offset+=INCREMENTAL_READ_BLOCK;
}
if (bytesRemaining>0)
{
lastHash=SuperFastHashIncremental (data+offset, bytesRemaining, lastHash );
}
return lastHash;
// return SuperFastHashIncremental(data,len,len);
}
unsigned int SuperFastHashIncremental (const char * data, int len, unsigned int lastHash )
{
__u32 hash = (__u32) lastHash;
__u32 tmp;
int rem;
if (len <= 0 || data == NULL) return 0;
rem = len & 3;
len >>= 2;
/* Main loop */
for (;len > 0; len--) {
hash += get16bits (data);
tmp = (get16bits (data+2) << 11) ^ hash;
hash = (hash << 16) ^ tmp;
data += 2*sizeof (__u16);
hash += hash >> 11;
}
/* Handle end cases */
switch (rem) {
case 3: hash += get16bits (data);
hash ^= hash << 16;
hash ^= data[sizeof (__u16)] << 18;
hash += hash >> 11;
break;
case 2: hash += get16bits (data);
hash ^= hash << 11;
hash += hash >> 17;
break;
case 1: hash += *data;
hash ^= hash << 10;
hash += hash >> 1;
}
/* Force "avalanching" of final 127 bits */
hash ^= hash << 3;
hash += hash >> 5;
hash ^= hash << 4;
hash += hash >> 17;
hash ^= hash << 25;
hash += hash >> 6;
return (unsigned int) hash;
}
unsigned int SuperFastHashFile (const char * filename)
{
FILE *fp = fopen(filename, "rb");
assert(fp);
if (fp==0)
return 0;
unsigned int hash = SuperFastHashFilePtr(fp);
fclose(fp);
return hash;
}
unsigned int SuperFastHashFilePtr (FILE *fp)
{
fseek(fp, 0, SEEK_END);
int length = (int)ftell(fp);
fseek(fp, 0, SEEK_SET);
int bytesRemaining=length;
unsigned int lastHash = length;
char readBlock[INCREMENTAL_READ_BLOCK];
while (bytesRemaining>=(int) sizeof(readBlock))
{
fread(readBlock, sizeof(readBlock), 1, fp);
lastHash=SuperFastHashIncremental (readBlock, (int) sizeof(readBlock), lastHash );
bytesRemaining-=(int) sizeof(readBlock);
}
if (bytesRemaining>0)
{
fread(readBlock, bytesRemaining, 1, fp);
lastHash=SuperFastHashIncremental (readBlock, bytesRemaining, lastHash );
}
return lastHash;
}