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/* $Id: jenkins.c 1530 2014-08-10 21:45:12Z coelho $ */
#include <stdint.h>
#define PN_32_1 433494437
#define PN_32_2 780291637
#define PN_32_3 1073676287
#define PN_32_4 1873012681
/* The following function is taken and adapted (wrt len) from
* http://www.burtleburtle.net/bob/hash/doobs.html,
* and is advertised public domain.
* This change breaks the incremental aspect of the computation.
*
* if hash==0, it is unchanged for the empty string.
*
* note: the jenkins function uses low-cost operators: + >> << ^
*/
static uint32_t jenkins_one_at_a_time_hash
(uint32_t hash, const unsigned char *key, size_t len)
{
size_t i;
for (i = 0; i < len; i++) {
hash += key[i] ^ len;
hash += (hash << 10);
hash ^= (hash >> 6);
}
hash += (hash << 3);
hash ^= (hash >> 11) + len;
hash += (hash << 15);
return hash;
}
/* checksum of sizes 2, 4 and 8.
* checksum_int?(NULL) == 0
* checksum_int?('') == some value
*/
static int16_t checksum_int2(const unsigned char *data, size_t size)
{
uint32_t h = 0; // default if NULL
if (data) h = jenkins_one_at_a_time_hash(PN_32_1, data, size);
return (int16_t) ((h>>16)^h);
}
// many collision, eg cksum4('16667') = cksum4('53827')
static int32_t checksum_int4(const unsigned char *data, size_t size)
{
uint32_t h = 0; // default if NULL
if (data) h = jenkins_one_at_a_time_hash(PN_32_2, data, size);
return (int32_t) h;
}
static int64_t checksum_int8(const unsigned char *data, size_t size)
{
uint64_t h1 = 0, h2 = 0; // default if NULL
if (data) {
// the 64 bit hash is based on two hashes. first one is chsum4
h1 = jenkins_one_at_a_time_hash(PN_32_3, data, size);
// ensure that size==0 => checksum==0
h2 = jenkins_one_at_a_time_hash(h1 ^ PN_32_4, data, size);
}
return (int64_t) ((h1<<32)|h2);
}
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