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authorIan Abbott <abbotti@mev.co.uk>2011-07-06 21:18:49 -0400
committerDavid S. Miller <davem@davemloft.net>2011-07-07 07:52:24 -0400
commitbe0e1e788b0973147b6b83cc940676cc26009eb7 (patch)
tree75083bdb5b5d9e266b0c632406d67f69505d527c /lib
parent97bc3633bec7ed0fdfbda6b9cf86c51e4f58f8e2 (diff)
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')
-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)
49 49
50static unsigned int do_csum(const unsigned char *buff, int len) 50static unsigned int do_csum(const unsigned char *buff, int len)
51{ 51{
52 int odd, count; 52 int odd;
53 unsigned int result = 0; 53 unsigned int result = 0;
54 54
55 if (len <= 0) 55 if (len <= 0)
@@ -64,25 +64,22 @@ static unsigned int do_csum(const unsigned char *buff, int len)
64 len--; 64 len--;
65 buff++; 65 buff++;
66 } 66 }
67 count = len >> 1; /* nr of 16-bit words.. */ 67 if (len >= 2) {
68 if (count) {
69 if (2 & (unsigned long) buff) { 68 if (2 & (unsigned long) buff) {
70 result += *(unsigned short *) buff; 69 result += *(unsigned short *) buff;
71 count--;
72 len -= 2; 70 len -= 2;
73 buff += 2; 71 buff += 2;
74 } 72 }
75 count >>= 1; /* nr of 32-bit words.. */ 73 if (len >= 4) {
76 if (count) { 74 const unsigned char *end = buff + ((unsigned)len & ~3);
77 unsigned int carry = 0; 75 unsigned int carry = 0;
78 do { 76 do {
79 unsigned int w = *(unsigned int *) buff; 77 unsigned int w = *(unsigned int *) buff;
80 count--;
81 buff += 4; 78 buff += 4;
82 result += carry; 79 result += carry;
83 result += w; 80 result += w;
84 carry = (w > result); 81 carry = (w > result);
85 } while (count); 82 } while (buff < end);
86 result += carry; 83 result += carry;
87 result = (result & 0xffff) + (result >> 16); 84 result = (result & 0xffff) + (result >> 16);
88 } 85 }