From: Alexey Dobriyan <adobriyan@gmail.com>
To: akpm@linux-foundation.org
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH] make isdigit() table lookupless
Date: Fri, 26 Aug 2016 22:00:47 +0300 [thread overview]
Message-ID: <20160826190047.GA12536@p183.telecom.by> (raw)
Make isdigit into a simple range checking inline function:
return '0' <= c && c <= '9';
This code is 1 branch, not 2 because any reasonable compiler can
optimize this code into SUB+CMP, so the code
while (isdigit((c = *s++)))
...
remains 1 branch per iteration HOWEVER it suddenly doesn't do table
lookup priming cacheline nobody cares about.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---
include/linux/ctype.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/include/linux/ctype.h
+++ b/include/linux/ctype.h
@@ -22,7 +22,10 @@ extern const unsigned char _ctype[];
#define isalnum(c) ((__ismask(c)&(_U|_L|_D)) != 0)
#define isalpha(c) ((__ismask(c)&(_U|_L)) != 0)
#define iscntrl(c) ((__ismask(c)&(_C)) != 0)
-#define isdigit(c) ((__ismask(c)&(_D)) != 0)
+static inline int isdigit(int c)
+{
+ return '0' <= c && c <= '9';
+}
#define isgraph(c) ((__ismask(c)&(_P|_U|_L|_D)) != 0)
#define islower(c) ((__ismask(c)&(_L)) != 0)
#define isprint(c) ((__ismask(c)&(_P|_U|_L|_D|_SP)) != 0)
reply other threads:[~2016-08-26 19:00 UTC|newest]
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