crc.c

#include <stdio.h>
#include <sys/types.h>
#include <math.h>
#include <string.h>
#include <stdlib.h>

#include "compat.h"


void crc32_table(uint32_t poly, uint32_t * table) {
  int i, j;

  for(i = 0; i < 256; i++) {
    table[i] = i;
    for(j = 8; j > 0; j--) {
      if(table[i] & 1)
        table[i] = (table[i] >> 1) ^ poly;
      else
        table[i] >>= 1;
    }
  }     
}

uint32_t crc_32(void * str, int length, uint32_t poly) {
  uint32_t table[256];
  int i;
  crc32_table(poly, table);
  uint32_t crc = 0xFFFFFFFF;

  for(i = 0 ; i < length ; i++) {
    crc = ( crc >> 8) ^ table[(((uint8_t *)str)[i] ^ crc) & 0x000000FF];
  }
  return ~crc;
}