lean2/src/util/hash.cpp
Leonardo de Moura ed3df178ac Improve hash for hierarchical names.
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
2013-07-24 14:56:32 -07:00

63 lines
2 KiB
C++

/*
Copyright (c) 2013 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Author: Leonardo de Moura
*/
namespace lean {
void mix(unsigned & a, unsigned & b, unsigned & 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);
}
// Bob Jenkin's hash function.
// http://burtleburtle.net/bob/hash/doobs.html
unsigned hash_str(unsigned length, char const * str, unsigned init_value) {
register unsigned a, b, c, len;
/* Set up the internal state */
len = length;
a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
c = init_value; /* the previous hash value */
/*---------------------------------------- handle most of the key */
while (len >= 12) {
a += reinterpret_cast<unsigned const *>(str)[0];
b += reinterpret_cast<unsigned const *>(str)[1];
c += reinterpret_cast<unsigned const *>(str)[2];
mix(a,b,c);
str += 12; len -= 12;
}
/*------------------------------------- handle the last 11 bytes */
c += length;
switch(len) {
/* all the case statements fall through */
case 11: c+=((unsigned)str[10]<<24);
case 10: c+=((unsigned)str[9]<<16);
case 9 : c+=((unsigned)str[8]<<8);
/* the first byte of c is reserved for the length */
case 8 : b+=((unsigned)str[7]<<24);
case 7 : b+=((unsigned)str[6]<<16);
case 6 : b+=((unsigned)str[5]<<8);
case 5 : b+=str[4];
case 4 : a+=((unsigned)str[3]<<24);
case 3 : a+=((unsigned)str[2]<<16);
case 2 : a+=((unsigned)str[1]<<8);
case 1 : a+=str[0];
/* case 0: nothing left to add */
}
mix(a,b,c);
/*-------------------------------------------- report the result */
return c;
}
}