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/*
* The contents of this file are public domain.
*
* Based on: lookup3.c, by Bob Jenkins, May 2006, Public Domain.
*/
#include "system.h"
#include "hash.h"
/*
* A simple version of Bob Jenkins' lookup3.c hash.
*
* It is supposed to give same results as hashlittle() on little-endian
* and hashbig() on big-endian machines.
*
* Speed seems comparable to Jenkins' optimized version (~ -10%).
* Actual difference varies as it depends on cpu/compiler/libc details.
*/
/* rotate uint32 */
#define rot(x,k) (((x)<<(k)) | ((x)>>(32-(k))))
/* mix 3 32-bit values reversibly */
#define mix(a, b, c) do { \
a -= c; a ^= rot(c, 4); c += b; \
b -= a; b ^= rot(a, 6); a += c; \
c -= b; c ^= rot(b, 8); b += a; \
a -= c; a ^= rot(c,16); c += b; \
b -= a; b ^= rot(a,19); a += c; \
c -= b; c ^= rot(b, 4); b += a; \
} while (0)
/* final mixing of 3 32-bit values (a,b,c) into c */
#define final(a, b, c) do { \
c ^= b; c -= rot(b,14); \
a ^= c; a -= rot(c,11); \
b ^= a; b -= rot(a,25); \
c ^= b; c -= rot(b,16); \
a ^= c; a -= rot(c, 4); \
b ^= a; b -= rot(a,14); \
c ^= b; c -= rot(b,24); \
} while (0)
/*
* GCC does not know how to optimize short variable-length copies.
* Its faster to do dumb inlined copy than call out to libc.
*/
static inline void simple_memcpy(void *dst_, const void *src_, size_t len)
{
const uint8_t *src = src_;
uint8_t *dst = dst_;
while (len--)
*dst++ = *src++;
}
/* short version - let compiler worry about memory access */
uint32_t lookup3_hash(const void *data, size_t len)
{
uint32_t a, b, c;
uint32_t buf[3];
const uint8_t *p = data;
a = b = c = 0xdeadbeef + len;
if (len == 0)
goto done;
while (len > 12) {
memcpy(buf, p, 12);
a += buf[0];
b += buf[1];
c += buf[2];
mix(a, b, c);
p += 12;
len -= 12;
}
buf[0] = buf[1] = buf[2] = 0;
simple_memcpy(buf, p, len);
a += buf[0];
b += buf[1];
c += buf[2];
final(a, b, c);
done:
return c;
}
/*
* Reversible integer hash function by Thomas Wang.
*/
uint32_t hash32(uint32_t v)
{
v = ~v + (v << 15);
v = v ^ (v >> 12);
v = v + (v << 2);
v = v ^ (v >> 4);
v = v * 2057;
v = v ^ (v >> 16);
return v;
}
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