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authorIan Abbott <abbotti@mev.co.uk>2011-07-07 01:18:49 +0000
committerDavid S. Miller <davem@davemloft.net>2011-07-07 04:52:24 -0700
commitbe0e1e788b0973147b6b83cc940676cc26009eb7 (patch)
tree75083bdb5b5d9e266b0c632406d67f69505d527c /lib/checksum.c
parent97bc3633bec7ed0fdfbda6b9cf86c51e4f58f8e2 (diff)
downloadlinux-be0e1e788b0973147b6b83cc940676cc26009eb7.tar.gz
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: Ian Abbott <abbotti@mev.co.uk> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'lib/checksum.c')
-rw-r--r--lib/checksum.c13
1 files changed, 5 insertions, 8 deletions
diff --git a/lib/checksum.c b/lib/checksum.c
index 097508732f34..8df2f91e6d98 100644
--- a/lib/checksum.c
+++ b/lib/checksum.c
@@ -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);
}