Commit 1204c77f authored Oct 11, 2016 by Alexey Dobriyan Committed by Linus Torvalds Oct 11, 2016

include/linux/ctype.h: make isdigit() table lookupless

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.

Link: http://lkml.kernel.org/r/20160826190047.GA12536@p183.telecom.by


Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bf90e56e

include/linux/ctype.h

+4 −1

Original line number	Diff line number	Diff line
		@@ -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)

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