63 lines
2 KiB
C++
63 lines
2 KiB
C++
/*
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Copyright (c) 2013 Microsoft Corporation. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Author: Leonardo de Moura
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*/
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namespace lean {
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void mix(unsigned & a, unsigned & b, unsigned & c) {
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a -= b; a -= c; a ^= (c>>13);
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b -= c; b -= a; b ^= (a<<8);
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c -= a; c -= b; c ^= (b>>13);
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a -= b; a -= c; a ^= (c>>12);
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b -= c; b -= a; b ^= (a<<16);
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c -= a; c -= b; c ^= (b>>5);
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a -= b; a -= c; a ^= (c>>3);
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b -= c; b -= a; b ^= (a<<10);
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c -= a; c -= b; c ^= (b>>15);
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}
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// Bob Jenkin's hash function.
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// http://burtleburtle.net/bob/hash/doobs.html
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unsigned hash_str(unsigned length, char const * str, unsigned init_value) {
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register unsigned a, b, c, len;
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/* Set up the internal state */
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len = length;
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a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
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c = init_value; /* the previous hash value */
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/*---------------------------------------- handle most of the key */
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while (len >= 12) {
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a += reinterpret_cast<unsigned const *>(str)[0];
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b += reinterpret_cast<unsigned const *>(str)[1];
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c += reinterpret_cast<unsigned const *>(str)[2];
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mix(a,b,c);
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str += 12; len -= 12;
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}
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/*------------------------------------- handle the last 11 bytes */
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c += length;
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switch(len) {
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/* all the case statements fall through */
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case 11: c+=((unsigned)str[10]<<24);
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case 10: c+=((unsigned)str[9]<<16);
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case 9 : c+=((unsigned)str[8]<<8);
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/* the first byte of c is reserved for the length */
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case 8 : b+=((unsigned)str[7]<<24);
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case 7 : b+=((unsigned)str[6]<<16);
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case 6 : b+=((unsigned)str[5]<<8);
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case 5 : b+=str[4];
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case 4 : a+=((unsigned)str[3]<<24);
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case 3 : a+=((unsigned)str[2]<<16);
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case 2 : a+=((unsigned)str[1]<<8);
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case 1 : a+=str[0];
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/* case 0: nothing left to add */
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}
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mix(a,b,c);
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/*-------------------------------------------- report the result */
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return c;
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}
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}
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