[PATCH] lib/checksum.c: optimize do_csum a bit
From: Ian Abbott <abbotti@mev.co.uk>
Date: 2011-07-07 11:19:14
Also in:
lkml
Subsystem:
library code, the rest · Maintainers:
Andrew Morton, Linus Torvalds
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> --- lib/checksum.c | 13 +++++-------- 1 files changed, 5 insertions(+), 8 deletions(-)
diff --git a/lib/checksum.c b/lib/checksum.c
index 0975087..8df2f91 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); }
--
1.7.6