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/*
* Produce a "generalized CRC" table. Assumes a platform with
* /dev/urandom -- otherwise reimplement get_random_byte().
*/
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
static uint8_t get_random_byte(void)
{
static int fd = -1;
uint8_t buf;
int rv;
if (fd < 0)
fd = open("/dev/urandom", O_RDONLY);
do {
errno = 0;
rv = read(fd, &buf, 1);
if (rv < 1 && errno != EAGAIN)
abort();
} while (rv < 1);
return buf;
}
static void random_permute(uint8_t *buf)
{
int i, j, k;
int m;
for (i = 0; i < 256; i++)
buf[i] = i;
m = 255;
for (i = 255; i > 0; i--) {
if (i <= (m >> 1))
m >>= 1;
do {
j = get_random_byte() & m;
} while (j > i);
k = buf[i];
buf[i] = buf[j];
buf[j] = k;
}
}
static void xcrc_table(uint64_t *buf)
{
uint8_t perm[256];
int i, j;
memset(buf, 0, 8*256); /* Make static checkers happy */
for (i = 0; i < 8; i++) {
random_permute(perm);
for (j = 0; j < 256; j++)
buf[j] = (buf[j] << 8) | perm[j];
}
}
int main(void)
{
int i;
uint64_t buf[256];
xcrc_table(buf);
for (i = 0; i < 256; i++) {
printf("%016"PRIx64"\n", buf[i]);
}
return 0;
}
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