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Commit be0e1e78 authored by Ian Abbott's avatar Ian Abbott Committed by David S. Miller
Browse files

lib/checksum.c: optimize do_csum a bit 



Reduce the number of variables modified by the loop in do_csum() by 1,
which seems like a good idea.  On Nios II (a RISC CPU with 3-operand
instruction set) it reduces the loop from 7 to 6 instructions, including
the conditional branch.

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 97bc3633

lib/checksum.c

+5 −8
Original line number Diff line number Diff line
@@ -49,7 +49,7 @@ static inline unsigned short from32to16(unsigned int x) 


static unsigned int do_csum(const unsigned char *buff, int len)

{

	int odd, count;

	int odd;

	unsigned int result = 0;



	if (len <= 0)
@@ -64,25 +64,22 @@ static unsigned int do_csum(const unsigned char *buff, int len) 
		len--;

		buff++;

	}

	count = len >> 1;		/* nr of 16-bit words.. */

	if (count) {

	if (len >= 2) {

		if (2 & (unsigned long) buff) {

			result += *(unsigned short *) buff;

			count--;

			len -= 2;

			buff += 2;

		}

		count >>= 1;		/* nr of 32-bit words.. */

		if (count) {

		if (len >= 4) {

			const unsigned char *end = buff + ((unsigned)len & ~3);

			unsigned int carry = 0;

			do {

				unsigned int w = *(unsigned int *) buff;

				count--;

				buff += 4;

				result += carry;

				result += w;

				carry = (w > result);

			} while (count);

			} while (buff < end);

			result += carry;

			result = (result & 0xffff) + (result >> 16);

		}