mirror of
https://github.com/cuberite/libdeflate.git
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bf50c64e86
"scripts" is a more descriptive name than "tools", which sounds too similar to "programs".
101 lines
3.2 KiB
C
101 lines
3.2 KiB
C
/*
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* gen_crc32_table.c - a program for CRC-32 table generation
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*
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* Originally public domain; changes after 2016-09-07 are copyrighted.
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*
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* Copyright 2016 Eric Biggers
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*
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* Permission is hereby granted, free of charge, to any person
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* obtaining a copy of this software and associated documentation
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* files (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use,
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* copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following
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* conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
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* OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
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* HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
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* WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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* OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include <stdint.h>
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#include <stdio.h>
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static uint32_t crc32_table[0x800];
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static uint32_t
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crc32_update_bit(uint32_t remainder, uint8_t next_bit)
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{
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return (remainder >> 1) ^
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(((remainder ^ next_bit) & 1) ? 0xEDB88320 : 0);
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}
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static uint32_t
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crc32_update_byte(uint32_t remainder, uint8_t next_byte)
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{
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for (int j = 0; j < 8; j++, next_byte >>= 1)
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remainder = crc32_update_bit(remainder, next_byte & 1);
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return remainder;
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}
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static void
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print_256_entries(const uint32_t *entries)
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{
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for (size_t i = 0; i < 256 / 4; i++) {
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printf("\t");
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for (size_t j = 0; j < 4; j++) {
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printf("0x%08x,", entries[i * 4 + j]);
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if (j != 3)
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printf(" ");
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}
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printf("\n");
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}
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}
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int
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main(void)
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{
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/* crc32_table[i] for 0 <= i < 0x100 is the CRC-32 of byte i. */
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for (int i = 0; i < 0x100; i++)
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crc32_table[i] = crc32_update_byte(0, i);
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/* crc32_table[i] for 0x100 <= i < 0x800 is the CRC-32 of byte i % 0x100
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* followed by i / 0x100 zero bytes. */
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for (int i = 0x100; i < 0x800; i++)
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crc32_table[i] = crc32_update_byte(crc32_table[i - 0x100], 0);
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printf("/*\n");
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printf(" * crc32_table.h - data table to accelerate CRC-32 computation\n");
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printf(" *\n");
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printf(" * THIS FILE WAS AUTOMATICALLY GENERATED "
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"BY gen_crc32_table.c. DO NOT EDIT.\n");
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printf(" */\n");
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printf("\n");
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printf("#include <stdint.h>\n");
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printf("\n");
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printf("static const uint32_t crc32_table[] = {\n");
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print_256_entries(&crc32_table[0x000]);
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printf("#if defined(CRC32_SLICE4) || defined(CRC32_SLICE8)\n");
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print_256_entries(&crc32_table[0x100]);
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print_256_entries(&crc32_table[0x200]);
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print_256_entries(&crc32_table[0x300]);
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printf("#endif /* CRC32_SLICE4 || CRC32_SLICE8 */\n");
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printf("#if defined(CRC32_SLICE8)\n");
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print_256_entries(&crc32_table[0x400]);
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print_256_entries(&crc32_table[0x500]);
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print_256_entries(&crc32_table[0x600]);
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print_256_entries(&crc32_table[0x700]);
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printf("#endif /* CRC32_SLICE8 */\n");
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printf("};\n");
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return 0;
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}
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