2020-07-03 10:31:22 +01:00
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/*
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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 Bj<EFBFBD>rn 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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2020-04-11 06:28:26 +01:00
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/* Standard CRC32 checksum: fast public domain implementation for
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* little-endian architectures. Written for compilation with an
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* optimizer set to perform loop unwinding. Outputs the checksum for
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* each file given as a command line argument. Invalid file names and
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* files that cause errors are silently skipped. The program reads
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* from stdin if it is called with no arguments. */
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2020-07-03 10:31:22 +01:00
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#include "utils.h"
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2020-04-11 06:28:26 +01:00
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u32 crc32_for_byte(u32 r)
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{
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for(int j = 0; j < 8; ++j) r = (r & 1 ? 0 : (u32)0xEDB88320L) ^ r >> 1;
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return r ^ (u32)0xFF000000L;
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}
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/* Any unsigned integer type with at least 32 bits may be used as
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* accumulator type for fast crc32-calulation, but unsigned long is
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* probably the optimal choice for most systems. */
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typedef unsigned long accum_t;
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void init_tables(u32 *table, u32 *wtable)
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{
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for(u64 i = 0; i < 0x100; ++i) table[i] = crc32_for_byte(i);
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for(u64 k = 0; k < sizeof(accum_t); ++k)
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{
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for(u64 w, i = 0; i < 0x100; ++i)
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{
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for(u64 j = w = 0; j < sizeof(accum_t); ++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 crc32(const void *data, u64 n_bytes, u32 *crc)
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{
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static u32 table[0x100], wtable[0x100 * sizeof(accum_t)];
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u64 n_accum = n_bytes / sizeof(accum_t);
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if (!*table) init_tables(table, wtable);
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for(u64 i = 0; i < n_accum; ++i)
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{
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accum_t a = *crc ^ ((accum_t*)data)[i];
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for(u64 j = *crc = 0; j < sizeof(accum_t); ++j) *crc ^= wtable[(j << 8) + (u8)(a >> 8 * j)];
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}
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for(u64 i = n_accum * sizeof(accum_t); i < n_bytes; ++i) *crc = table[(u8)*crc ^ ((u8*)data)[i]] ^ *crc >> 8;
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}
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