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crcgen: utility program to generate CRC tables

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Small utility program to generate CRC tables in both C and Perl
formats.  Note: we don't actually need a true CRC, which is what this
generates.  We may want to consider going to a "generalized CRC",
meaning a randomly generated set of 8 bytewise permutations.  These
have the advantage of not being linear, while having the same software
implementation as a true CRC.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2009-07-16 10:20:14 -04:00
parent 80d0fd371f
commit 395d381114
1 changed files with 47 additions and 0 deletions
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misc/crcgen.c Normal file
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#include <inttypes.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
/* Polynomial in bit-reversed notation */
uint64_t poly;
uint64_t crctab[256], v;
int i, j;
poly = strtoumax(argv[1], NULL, 0);
printf("/* C */\n");
printf("static const uint64_t crc64_tab[256] = {\n");
for (i = 0; i < 256; i++) {
v = i;
for (j = 0; j < 8; j++)
v = (v >> 1) ^ ((v & 1) ? poly : 0);
crctab[i] = v;
}
for (i = 0; i < 256; i += 2) {
printf(" /* %02x */ UINT64_C(0x%016"PRIx64"), "
"UINT64_C(0x%016"PRIx64")%s\n",
i, crctab[i], crctab[i+1], (i == 254) ? "" : ",");
}
printf("};\n\n");
printf("# perl\n");
printf("@crc64_tab = (\n");
for (i = 0; i < 256; i += 2) {
printf(" [0x%08"PRIx32", 0x%08"PRIx32"], "
"[0x%08"PRIx32", 0x%08"PRIx32"]%-1s # %02x\n",
(uint32_t)(crctab[i] >> 32),
(uint32_t)(crctab[i]),
(uint32_t)(crctab[i+1] >> 32),
(uint32_t)(crctab[i+1]),
(i == 254) ? "" : ",",
i);
}
printf(");\n");
return 0;
}