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/* crc-generate-table.c -- cyclic redundancy check table generator
Copyright (C) 2024-2025 Free Software Foundation, Inc.
This file is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.
This file is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Sam Russell. */
#include <stdio.h>
#include <stdlib.h>
/*
* The following function was extracted from RFC 1952 by Sam
* Russell. It was modified to remove the reference to the
* crc_table_computed flag, to extend it to accept a variable number
* of bits (described below), and reformatted to follow GNU
* formatting guidelines.
*
* make_crc_table() takes a number of bits and generates a lookup
* table for the CRC32 algorithm. Usage is as follows:
*
* make_crc_table(8) : generate for CRC32(0x00) to CRC32(0xFF)
* make_crc_table(16) : generate for CRC32(0x0000) to CRC32 (0xFF00)
* in increments of 0x100
*
* This is used for the Sarwate algorithm specified in RFC 1952
* which uses a single lookup table of make_crc_table(8), and for
* the slice-by-8 algorithm which uses 8 tables from in 8-bit
* increments from make_crc_table(8) to make_crc_table(64)
*/
unsigned long crc_table[256];
static void
make_crc_table (int bits)
{
unsigned long c;
int n, k;
for (n = 0; n < 256; n++)
{
c = (unsigned long) n;
for (k = 0; k < bits; k++)
{
if (c & 1)
c = 0xedb88320L ^ (c >> 1);
else
c = c >> 1;
}
crc_table[n] = c;
}
}
static void
print_crc_table (FILE * stream, int bits)
{
make_crc_table (bits);
fprintf (stream, " {");
for (int i = 0; i < 256; i++)
{
if ((i % 6) == 0)
fprintf (stream, "\n ");
if (i != 255)
fprintf (stream, " 0x%08lX,", crc_table[i]);
else
fprintf (stream, " 0x%08lX\n", crc_table[i]);
}
fprintf (stream, " }");
}
static void
print_header (FILE * stream)
{
fprintf (stream, "/* Slice-by-8 lookup tables */\n");
fprintf (stream, "static const uint32_t crc32_sliceby8_table[][256] = {\n");
for (int i = 8; i <= 64; i += 8)
{
print_crc_table (stream, i);
if (i < 64)
fprintf (stream, ",");
fprintf (stream, "\n");
}
fprintf (stream, "};\n");
}
static void
print_copyright_notice (FILE * stream)
{
fprintf (stream, "/* DO NOT EDIT! GENERATED AUTOMATICALLY! */\n");
fprintf (stream, "/* crc.c -- cyclic redundancy checks\n");
fprintf (stream,
"Copyright (C) 2005-2006, 2009-2025 Free Software Foundation, Inc.\n");
fprintf (stream, "\n");
fprintf (stream,
"This file is free software: you can redistribute it and/or modify\n");
fprintf (stream,
"it under the terms of the GNU Lesser General Public License as\n");
fprintf (stream,
"published by the Free Software Foundation, either version 3 of the\n");
fprintf (stream, "License, or (at your option) any later version.\n");
fprintf (stream, "\n");
fprintf (stream,
"This file is distributed in the hope that it will be useful,\n");
fprintf (stream,
"but WITHOUT ANY WARRANTY; without even the implied warranty of\n");
fprintf (stream,
"MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the\n");
fprintf (stream, "GNU Lesser General Public License for more details.\n");
fprintf (stream, "\n");
fprintf (stream,
"You should have received a copy of the GNU Lesser General Public License\n");
fprintf (stream,
"along with this program. If not, see <https://www.gnu.org/licenses/>. */\n\n");
}
int
main (int argc, char *argv[])
{
if (argc != 2)
{
fprintf (stderr, " Usage: %s crc-sliceby8.h\n", argv[0]);
exit (1);
}
const char *filename = argv[1];
FILE *stream = fopen (filename, "w");
if (stream == NULL)
{
fprintf (stderr, "cannot open '%s' for writing\n", filename);
exit (1);
}
print_copyright_notice (stream);
print_header (stream);
if (ferror (stream) || fclose (stream))
{
fprintf (stderr, "error writing to '%s'\n", filename);
exit (1);
}
return 0;
}
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