Question

I have the follow CRC function:

unsigned long Checksummer::crc32 (unsigned long crc, char *buf, unsigned long len)
{
   unsigned long crc_table[256];
   int i, k;
   for (i = 0; i < 256; i++) {
      unsigned long c = (unsigned long) i;
      for (k = 0; k < 8; k++) 
         c = c & 1 ? 0xedb88320 ^ (c >> 1) : c >> 1;
      crc_table[i] = c;
   }

   crc = crc ^ 0xffffffffL;
   while (len--) 
      crc = crc_table[((int)crc ^ (*buf++)) & 0xff] ^ (crc >> 8);
   return crc ^ 0xffffffffL;
}

I am trying to port this code to Java so that I can calculate CRCs on multiple platforms. My ported code below produces a different result. What am I doing wrong?

static long getCrc32 (long crc, char[] buf, long len)
{
   long crc_table[] = new long[256];
   int i, k;
   for (i = 0; i < 256; i++) {
      long c = ( long)i;
      for (k = 0; k < 8; k++) 
         c = (c & 1) == 1 ? 0xedb88320 ^ (c >> 1) : c >> 1;
      crc_table[i] = c;
    }

    /* Calculate crc on buf */
    crc = crc ^ 0xffffffffL;
    int j = 0;
    while (len-- != 0){ 
       crc = crc_table[((int)crc ^ (buf[(int)j++])) & 0xff] ^ (crc >> 8);}
    return crc ^ 0xffffffffL;
}

Answer 1

char is two bytes in Java; use byte instead (char in C and C++ are one byte by definition).

long is eight bytes in Java; use int instead (assuming sizeof(unsigned long) == 4 on your C++ platform, which is the norm).