forked from dolphin-emu/dolphin
c86d2e5129
git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@3898 8ced0084-cf51-0410-be5f-012b33b47a6e
137 lines
2.8 KiB
C++
137 lines
2.8 KiB
C++
// Copyright (C) 2003 Dolphin Project.
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, version 2.0.
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License 2.0 for more details.
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// A copy of the GPL 2.0 should have been included with the program.
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// If not, see http://www.gnu.org/licenses/
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// Official SVN repository and contact information can be found at
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// http://code.google.com/p/dolphin-emu/
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#include "Hash.h"
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// uint32_t
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// WARNING - may read one more byte!
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// Implementation from Wikipedia.
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u32 HashFletcher(const u8* data_u8, size_t length)
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{
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const u16* data = (const u16*)data_u8; /* Pointer to the data to be summed */
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size_t len = (length + 1) / 2; /* Length in 16-bit words */
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u32 sum1 = 0xffff, sum2 = 0xffff;
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while (len)
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{
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size_t tlen = len > 360 ? 360 : len;
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len -= tlen;
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do {
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sum1 += *data++;
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sum2 += sum1;
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}
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while (--tlen);
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sum1 = (sum1 & 0xffff) + (sum1 >> 16);
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sum2 = (sum2 & 0xffff) + (sum2 >> 16);
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}
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// Second reduction step to reduce sums to 16 bits
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sum1 = (sum1 & 0xffff) + (sum1 >> 16);
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sum2 = (sum2 & 0xffff) + (sum2 >> 16);
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return(sum2 << 16 | sum1);
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}
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// Implementation from Wikipedia
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// Slightly slower than Fletcher above, but slighly more reliable.
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#define MOD_ADLER 65521
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// data: Pointer to the data to be summed; len is in bytes
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u32 HashAdler32(const u8* data, size_t len)
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{
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u32 a = 1, b = 0;
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while (len)
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{
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size_t tlen = len > 5550 ? 5550 : len;
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len -= tlen;
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do
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{
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a += *data++;
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b += a;
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}
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while (--tlen);
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a = (a & 0xffff) + (a >> 16) * (65536 - MOD_ADLER);
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b = (b & 0xffff) + (b >> 16) * (65536 - MOD_ADLER);
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}
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// It can be shown that a <= 0x1013a here, so a single subtract will do.
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if (a >= MOD_ADLER)
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{
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a -= MOD_ADLER;
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}
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// It can be shown that b can reach 0xfff87 here.
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b = (b & 0xffff) + (b >> 16) * (65536 - MOD_ADLER);
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if (b >= MOD_ADLER)
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{
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b -= MOD_ADLER;
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}
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return((b << 16) | a);
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}
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// Another fast and decent hash
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u32 HashFNV(const u8* ptr, int length)
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{
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u32 hash = 0x811c9dc5;
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for (int i = 0; i < length; i++)
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{
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hash *= 1677761;
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hash ^= ptr[i];
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}
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return(hash);
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}
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// Another fast and decent hash
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u32 HashFNV1(const u8* ptr, int length)
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{
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u32 hash = 0x811c9dc5;
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for (int i = 0; i < length; i++)
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{
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hash *= 1677761;
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hash ^= ptr[i];
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}
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return(hash);
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}
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// Stupid hash - but can't go back now :)
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// Don't use for new things. At least it's reasonably fast.
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u32 HashEctor(const u8* ptr, int length)
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{
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u32 crc = 0;
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for (int i = 0; i < length; i++)
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{
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crc ^= ptr[i];
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crc = (crc << 3) | (crc >> 29);
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}
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return(crc);
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}
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