mirror of
https://github.com/DarkMatterCore/nxdumptool.git
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62 lines
2.1 KiB
C
62 lines
2.1 KiB
C
/*
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* crc32_fast.c
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*
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* Based on the standard CRC32 checksum fast public domain implementation for
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* little-endian architecures by Björn Samuelsson (http://home.thep.lu.se/~bjorn/crc).
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*
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* Copyright (c) 2020, DarkMatterCore <pabloacurielz@gmail.com>.
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*
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* This file is part of nxdumptool (https://github.com/DarkMatterCore/nxdumptool).
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*
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* nxdumptool is free software; you can redistribute it and/or modify it
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* under the terms and conditions of the GNU General Public License,
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* version 2, as published by the Free Software Foundation.
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*
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* nxdumptool is distributed in the hope it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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* more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "utils.h"
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static u32 crc32FastGetTableValueByIndex(u32 r)
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{
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for(u32 j = 0; j < 8; ++j) r = ((r & 1 ? 0 : (u32)0xEDB88320) ^ r >> 1);
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return (r ^ (u32)0xFF000000);
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}
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static void crc32FastInitializeTables(u32 *table, u32 *wtable)
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{
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for(u32 i = 0; i < 0x100; ++i) table[i] = crc32FastGetTableValueByIndex(i);
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for(u32 k = 0; k < 4; ++k)
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{
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for(u32 w, i = 0; i < 0x100; ++i)
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{
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for(u32 j = w = 0; j < 4; ++j) w = (table[(u8)(j == k ? (w ^ i) : w)] ^ w >> 8);
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wtable[(k << 8) + i] = (w ^ (k ? wtable[0] : 0));
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}
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}
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}
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void crc32FastCalculate(const void *data, u64 n_bytes, u32 *crc)
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{
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if (!data || !n_bytes || !crc) return;
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static u32 table[0x100] = {0}, wtable[0x400] = {0};
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u64 n_accum = (n_bytes / 4);
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if (!*table) crc32FastInitializeTables(table, wtable);
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for(u64 i = 0; i < n_accum; ++i)
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{
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u32 a = (*crc ^ ((const u32*)data)[i]);
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for(u32 j = *crc = 0; j < 4; ++j) *crc ^= wtable[(j << 8) + (u8)(a >> 8 * j)];
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}
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for(u64 i = (n_accum * 4); i < n_bytes; ++i) *crc = (table[(u8)*crc ^ ((const u8*)data)[i]] ^ *crc >> 8);
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}
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