决定这通常足够有用,可以编写和提供:
#include <stdio.h>
#include <inttypes.h>
#include <assert.h>
#include <pthread.h>
#define POLY UINT64_C(0xc96c5795d7870f42)
static uint64_t crc64_little_table[8][256];
static uint64_t crc64_big_table[8][256];
static void crc64_init(uint64_t table[][256])
{
unsigned n, k;
uint64_t crc;
for (n = 0; n < 256; n++) {
crc = n;
for (k = 0; k < 8; k++)
crc = crc & 1 ? POLY ^ (crc >> 1) : crc >> 1;
table[0][n] = crc;
}
for (n = 0; n < 256; n++) {
crc = table[0][n];
for (k = 1; k < 8; k++) {
crc = table[0][crc & 0xff] ^ (crc >> 8);
table[k][n] = crc;
}
}
}
static void crc64_little_init(void)
{
crc64_init(crc64_little_table);
}
static inline uint64_t rev8(uint64_t a)
{
uint64_t m;
m = UINT64_C(0xff00ff00ff00ff);
a = ((a >> 8) & m) | (a & m) << 8;
m = UINT64_C(0xffff0000ffff);
a = ((a >> 16) & m) | (a & m) << 16;
return a >> 32 | a << 32;
}
static void crc64_big_init(void)
{
unsigned k, n;
crc64_init(crc64_big_table);
for (k = 0; k < 8; k++)
for (n = 0; n < 256; n++)
crc64_big_table[k][n] = rev8(crc64_big_table[k][n]);
}
#ifdef PTHREAD_ONCE_INIT
# define ONCE(init) \
do { \
static pthread_once_t once = PTHREAD_ONCE_INIT; \
pthread_once(&once, init); \
} while (0)
#else
# define ONCE(init) \
do { \
static volatile int once = 1; \
if (once) { \
if (once++ == 1) { \
init(); \
once = 0; \
} \
else \
while (once) \
; \
} \
} while (0)
#endif
static inline uint64_t crc64_little(uint64_t crc, void *buf, size_t len)
{
unsigned char *next = buf;
ONCE(crc64_little_init);
crc = ~crc;
while (len && ((uintptr_t)next & 7) != 0) {
crc = crc64_little_table[0][(crc ^ *next++) & 0xff] ^ (crc >> 8);
len--;
}
while (len >= 8) {
crc ^= *(uint64_t *)next;
crc = crc64_little_table[7][crc & 0xff] ^
crc64_little_table[6][(crc >> 8) & 0xff] ^
crc64_little_table[5][(crc >> 16) & 0xff] ^
crc64_little_table[4][(crc >> 24) & 0xff] ^
crc64_little_table[3][(crc >> 32) & 0xff] ^
crc64_little_table[2][(crc >> 40) & 0xff] ^
crc64_little_table[1][(crc >> 48) & 0xff] ^
crc64_little_table[0][crc >> 56];
next += 8;
len -= 8;
}
while (len) {
crc = crc64_little_table[0][(crc ^ *next++) & 0xff] ^ (crc >> 8);
len--;
}
return ~crc;
}
static inline uint64_t crc64_big(uint64_t crc, void *buf, size_t len)
{
unsigned char *next = buf;
ONCE(crc64_big_init);
crc = ~rev8(crc);
while (len && ((uintptr_t)next & 7) != 0) {
crc = crc64_big_table[0][(crc >> 56) ^ *next++] ^ (crc << 8);
len--;
}
while (len >= 8) {
crc ^= *(uint64_t *)next;
crc = crc64_big_table[0][crc & 0xff] ^
crc64_big_table[1][(crc >> 8) & 0xff] ^
crc64_big_table[2][(crc >> 16) & 0xff] ^
crc64_big_table[3][(crc >> 24) & 0xff] ^
crc64_big_table[4][(crc >> 32) & 0xff] ^
crc64_big_table[5][(crc >> 40) & 0xff] ^
crc64_big_table[6][(crc >> 48) & 0xff] ^
crc64_big_table[7][crc >> 56];
next += 8;
len -= 8;
}
while (len) {
crc = crc64_big_table[0][(crc >> 56) ^ *next++] ^ (crc << 8);
len--;
}
return ~rev8(crc);
}
uint64_t crc64(uint64_t crc, void *buf, size_t len)
{
uint64_t n = 1;
return *(char *)&n ? crc64_little(crc, buf, len) :
crc64_big(crc, buf, len);
}
#define GF2_DIM 64
static uint64_t gf2_matrix_times(uint64_t *mat, uint64_t vec)
{
uint64_t sum;
sum = 0;
while (vec) {
if (vec & 1)
sum ^= *mat;
vec >>= 1;
mat++;
}
return sum;
}
static void gf2_matrix_square(uint64_t *square, uint64_t *mat)
{
unsigned n;
for (n = 0; n < GF2_DIM; n++)
square[n] = gf2_matrix_times(mat, mat[n]);
}
uint64_t crc64_combine(uint64_t crc1, uint64_t crc2, uintmax_t len2)
{
unsigned n;
uint64_t row;
uint64_t even[GF2_DIM];
uint64_t odd[GF2_DIM];
if (len2 == 0)
return crc1;
odd[0] = POLY;
row = 1;
for (n = 1; n < GF2_DIM; n++) {
odd[n] = row;
row <<= 1;
}
gf2_matrix_square(even, odd);
gf2_matrix_square(odd, even);
do {
gf2_matrix_square(even, odd);
if (len2 & 1)
crc1 = gf2_matrix_times(even, crc1);
len2 >>= 1;
if (len2 == 0)
break;
gf2_matrix_square(odd, even);
if (len2 & 1)
crc1 = gf2_matrix_times(odd, crc1);
len2 >>= 1;
} while (len2 != 0);
crc1 ^= crc2;
return crc1;
}
static void crc64_test(void *vector, size_t len, uint64_t crc)
{
uint64_t crc1, crc2;
crc1 = crc64(0, vector, len);
if (crc1 ^ crc)
printf("mismatch: %" PRIx64 ", should be %" PRIx64 "\n", crc1, crc);
crc1 = crc64(0, vector, (len + 1) >> 1);
crc2 = crc64(0, vector + ((len + 1) >> 1), len >> 1);
crc1 = crc64_combine(crc1, crc2, len >> 1);
if (crc1 ^ crc)
printf("mismatch: %" PRIx64 ", should be %" PRIx64 "\n", crc1, crc);
}
#define TEST1 "123456789"
#define TESTLEN1 9
#define TESTCRC1 UINT64_C(0x995dc9bbdf1939fa)
#define TEST2 "This is a test of the emergency broadcast system."
#define TESTLEN2 49
#define TESTCRC2 UINT64_C(0x27db187fc15bbc72)
int main(void)
{
crc64_test(TEST1, TESTLEN1, TESTCRC1);
crc64_test(TEST2, TESTLEN2, TESTCRC2);
return 0;
}