Optimized ether_crc32_be()
John Baldwin
jhb at FreeBSD.org
Tue Jun 22 21:11:21 GMT 2004
On Friday 18 June 2004 07:37 pm, Christian Weisgerber wrote:
> Taken from kern/49957, here's a table-driven implementation of
> ether_crc32_be() to complement the little-endian one. For 6-byte
> MAC addresses it's about five times faster than the double loop.
>
> Comments?
Doesn't look like anyone responded. Perhaps ask someone on sparc64 to test it
along with some simple multicast test? (Use mtest to join a group, turn on
bmcastecho and then ping the multicast group to see if it responds?)
> Index: net/if_ethersubr.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/net/if_ethersubr.c,v
> retrieving revision 1.172
> diff -u -r1.172 if_ethersubr.c
> --- net/if_ethersubr.c 15 Jun 2004 23:57:41 -0000 1.172
> +++ net/if_ethersubr.c 18 Jun 2004 23:28:37 -0000
> @@ -883,9 +883,8 @@
>
> #if 0
> /*
> - * This is for reference. We have a table-driven version
> - * of the little-endian crc32 generator, which is faster
> - * than the double-loop.
> + * This is for reference. We have table-driven versions of the
> + * crc32 generators, which are faster than the double-loop.
> */
> uint32_t
> ether_crc32_le(const uint8_t *buf, size_t len)
> @@ -907,6 +906,28 @@
>
> return (crc);
> }
> +
> +uint32_t
> +ether_crc32_be(const uint8_t *buf, size_t len)
> +{
> + size_t i;
> + uint32_t crc, carry;
> + int bit;
> + uint8_t data;
> +
> + crc = 0xffffffff; /* initial value */
> +
> + for (i = 0; i < len; i++) {
> + for (data = *buf++, bit = 0; bit < 8; bit++, data >>= 1) {
> + carry = ((crc & 0x80000000) ? 1 : 0) ^ (data & 0x01);
> + crc <<= 1;
> + if (carry)
> + crc = (crc ^ ETHER_CRC_POLY_BE) | carry;
> + }
> + }
> +
> + return (crc);
> +}
> #else
> uint32_t
> ether_crc32_le(const uint8_t *buf, size_t len)
> @@ -930,29 +951,35 @@
>
> return (crc);
> }
> -#endif
>
> uint32_t
> ether_crc32_be(const uint8_t *buf, size_t len)
> {
> + static const uint8_t rev[] = {
> + 0x0, 0x8, 0x4, 0xc, 0x2, 0xa, 0x6, 0xe,
> + 0x1, 0x9, 0x5, 0xd, 0x3, 0xb, 0x7, 0xf
> + };
> + static const uint32_t crctab[] = {
> + 0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9,
> + 0x130476dc, 0x17c56b6b, 0x1a864db2, 0x1e475005,
> + 0x2608edb8, 0x22c9f00f, 0x2f8ad6d6, 0x2b4bcb61,
> + 0x350c9b64, 0x31cd86d3, 0x3c8ea00a, 0x384fbdbd
> + };
> size_t i;
> - uint32_t crc, carry;
> - int bit;
> + uint32_t crc;
> uint8_t data;
>
> crc = 0xffffffff; /* initial value */
>
> for (i = 0; i < len; i++) {
> - for (data = *buf++, bit = 0; bit < 8; bit++, data >>= 1) {
> - carry = ((crc & 0x80000000) ? 1 : 0) ^ (data & 0x01);
> - crc <<= 1;
> - if (carry)
> - crc = (crc ^ ETHER_CRC_POLY_BE) | carry;
> - }
> + data = buf[i];
> + crc = (crc << 4) ^ crctab[(crc >> 28) ^ rev[data & 0xf]];
> + crc = (crc << 4) ^ crctab[(crc >> 28) ^ rev[data >> 4]];
> }
>
> return (crc);
> }
> +#endif
>
> int
> ether_ioctl(struct ifnet *ifp, int command, caddr_t data)
--
John Baldwin <jhb at FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
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