php crc32算法

crc32.c

      char *p;
      int len, nr;           
      php_uint32 crcinit = 0;
      register php_uint32 crc;
    
      if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "s", &p, &nr) == FAILURE) {
          return;            
      }
      crc = crcinit^0xFFFFFFFF;
    
      for (len =+nr; nr--; ++p) {
          crc = ((crc >> 8) & 0x00FFFFFF) ^ crc32tab[(crc ^ (*p)) & 0xFF ]; 
      }
      RETVAL_LONG(crc^0xFFFFFFFF);