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7d3e2a997c
I've decided to simplify and standardize the licensing status for the library by using the MIT license instead of CC0 (a.k.a. "public domain"). This eliminates the somewhat controversial 4(a) clause in CC0, and, for this and other reasons, should (somewhat ironically) make it easier for some people to use and contribute to the project. Note: copyright will apply to new changes and to new versions of the work as a whole. Of course, versions previously released as public domain remain public domain where legally recognized.
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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