c - _mm_crc32_u8 gives different result than reference code -

i've been struggling intrinsics. in particular don't same results using standard crc calculation , supposedly equivalent intel intrinsics. i'd move using _mm_crc32_u16, , _mm_crc32_u32 if can't 8 bit operation work there's no point.

static uint32               g_ui32crc32table[256] = {     0x00000000l, 0x77073096l, 0xee0e612cl, 0x990951bal,     0x076dc419l, 0x706af48fl, 0xe963a535l, 0x9e6495a3l,     0x0edb8832l, 0x79dcb8a4l, 0xe0d5e91el, 0x97d2d988l, ....  // basic 32-bit crc calculator // note: code cannot changed uint32 calccrc32(unsigned char *pucbuff, int ilen) {     uint32 crc = 0xffffffff;      (int x = 0; x < ilen; x++)     {         crc = g_ui32crc32table[(crc ^ *pucbuff++) & 0xffl] ^ (crc >> 8);     }      return crc ^ 0xffffffff; }   uint32 calccrc32_intrinsic(unsigned char *pucbuff, int ilen) {     uint32 crc = 0xffffffff;      (int x = 0; x < ilen; x++)     {         crc = _mm_crc32_u8(crc, *pucbuff++);     }     return crc ^ 0xffffffff; } 

that table different crc polynomial 1 used intel instruction. table ethernet/zip/etc. crc, referred crc-32. intel instruction uses iscsi (castagnoli) polynomial, crc referred crc-32c.

this short example code can calculate either, uncommenting desired polynomial:

#include <stddef.h> #include <stdint.h>  /* crc-32 (ethernet, zip, etc.) polynomial in reversed bit order. */ #define poly 0xedb88320  /* crc-32c (iscsi) polynomial in reversed bit order. */ /* #define poly 0x82f63b78 */  /* compute crc of buf[0..len-1] initial crc crc.  permits    computation of crc feeding routine chunk of input data @    time.  value of crc first chunk should zero. */ uint32_t crc32c(uint32_t crc, const unsigned char *buf, size_t len) {     int k;      crc = ~crc;     while (len--) {         crc ^= *buf++;         (k = 0; k < 8; k++)             crc = crc & 1 ? (crc >> 1) ^ poly : crc >> 1;     }     return ~crc; } 

you can use code generate replacement table code computing crc-32c of each of one-byte messages 0, 1, 2, ..., 255.