Re: beta testing version

"Mikheev, Vadim" <vmikheev(at)SECTORBASE(dot)COM> writes:
> This may be implemented very fast (if someone points me where
> I can find CRC func).

Lifted from the PNG spec (RFC 2083):

15. Appendix: Sample CRC Code

The following sample code represents a practical implementation of
the CRC (Cyclic Redundancy Check) employed in PNG chunks. (See also
ISO 3309 [ISO-3309] or ITU-T V.42 [ITU-V42] for a formal
specification.)

/* Make the table for a fast CRC. */
void make_crc_table(void)
{
unsigned long c;
int n, k;
for (n = 0; n < 256; n++) {
c = (unsigned long) n;
for (k = 0; k < 8; k++) {
if (c & 1)
c = 0xedb88320L ^ (c >> 1);
else
c = c >> 1;
}
crc_table[n] = c;
}
crc_table_computed = 1;
}

/* Update a running CRC with the bytes buf[0..len-1]--the CRC
should be initialized to all 1's, and the transmitted value
is the 1's complement of the final running CRC (see the
crc() routine below)). */

unsigned long update_crc(unsigned long crc, unsigned char *buf,
int len)
{
unsigned long c = crc;
int n;

if (!crc_table_computed)
make_crc_table();
for (n = 0; n < len; n++) {
c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
}
return c;
}

/* Return the CRC of the bytes buf[0..len-1]. */
unsigned long crc(unsigned char *buf, int len)
{
return update_crc(0xffffffffL, buf, len) ^ 0xffffffffL;
}

regards, tom lane