From 15ae02baf025750cd79ef3929c28f7083a088bd2 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 6 Feb 2008 01:37:49 -0800 Subject: [PATCH] lib/extable.c: remove an expensive integer divide in search_extable() Actual code let compiler generates idiv instruction on x86. Using a right shift is OK here and readable as well. Before patch 10: 57 push %edi 11: 56 push %esi 12: 89 d6 mov %edx,%esi 14: 53 push %ebx 15: 89 c3 mov %eax,%ebx 17: eb 22 jmp 3b 19: 89 f0 mov %esi,%eax 1b: ba 02 00 00 00 mov $0x2,%edx 20: 29 d8 sub %ebx,%eax 22: 89 d7 mov %edx,%edi 24: c1 f8 03 sar $0x3,%eax 27: 99 cltd 28: f7 ff idiv %edi 2a: 8d 04 c3 lea (%ebx,%eax,8),%eax 2d: 39 08 cmp %ecx,(%eax) ... After patch 00000010 : 10: 53 push %ebx 11: 89 c3 mov %eax,%ebx 13: eb 18 jmp 2d 15: 89 d0 mov %edx,%eax 17: 29 d8 sub %ebx,%eax 19: c1 f8 04 sar $0x4,%eax 1c: 8d 04 c3 lea (%ebx,%eax,8),%eax 1f: 39 08 cmp %ecx,(%eax) ... Signed-off-by: Eric Dumazet Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/extable.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/lib/extable.c b/lib/extable.c index 463f4560f16d..179c08745595 100644 --- a/lib/extable.c +++ b/lib/extable.c @@ -57,10 +57,10 @@ search_extable(const struct exception_table_entry *first, while (first <= last) { const struct exception_table_entry *mid; - mid = (last - first) / 2 + first; + mid = ((last - first) >> 1) + first; /* - * careful, the distance between entries can be - * larger than 2GB: + * careful, the distance between value and insn + * can be larger than MAX_LONG: */ if (mid->insn < value) first = mid + 1;