diff options
| author | Rasmus Villemoes <linux@rasmusvillemoes.dk> | 2015-04-16 02:17:02 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2015-04-16 02:35:23 +0300 |
| commit | 51be17dfff753e72872f096ce1e654734f2fec50 (patch) | |
| tree | ce599aed4449d1357479ae4c07a6100fdc625a40 /lib | |
| parent | 7b1460eccad0621e0c48f52bbedeb7adddc55ac9 (diff) | |
| download | linux-51be17dfff753e72872f096ce1e654734f2fec50.tar.xz | |
lib/vsprintf.c: eliminate some branches
Since FORMAT_TYPE_INT is simply 1 more than FORMAT_TYPE_UINT, and
similarly for BYTE/UBYTE, SHORT/USHORT, LONG/ULONG, we can eliminate a few
instructions by making SIGN have the value 1 instead of 2, and then use
arithmetic instead of branches for computing the right spec->type. It's a
little hacky, but certainly in the same spirit as SMALL needing to have
the value 0x20. For example for the spec->qualifier == 'l' case, gcc now
generates
75e: 0f b6 53 01 movzbl 0x1(%rbx),%edx
762: 83 e2 01 and $0x1,%edx
765: 83 c2 09 add $0x9,%edx
768: 88 13 mov %dl,(%rbx)
instead of
763: 0f b6 53 01 movzbl 0x1(%rbx),%edx
767: 83 e2 02 and $0x2,%edx
76a: 80 fa 01 cmp $0x1,%dl
76d: 19 d2 sbb %edx,%edx
76f: 83 c2 0a add $0xa,%edx
772: 88 13 mov %dl,(%rbx)
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/vsprintf.c | 30 |
1 files changed, 11 insertions, 19 deletions
diff --git a/lib/vsprintf.c b/lib/vsprintf.c index b235c96167d3..318d583fe862 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -340,8 +340,8 @@ int num_to_str(char *buf, int size, unsigned long long num) return len; } -#define ZEROPAD 1 /* pad with zero */ -#define SIGN 2 /* unsigned/signed long */ +#define SIGN 1 /* unsigned/signed, must be 1 */ +#define ZEROPAD 2 /* pad with zero */ #define PLUS 4 /* show plus */ #define SPACE 8 /* space if plus */ #define LEFT 16 /* left justified */ @@ -447,7 +447,7 @@ char *number(char *buf, char *end, unsigned long long num, spec.precision = i; /* leading space padding */ spec.field_width -= spec.precision; - if (!(spec.flags & (ZEROPAD+LEFT))) { + if (!(spec.flags & (ZEROPAD | LEFT))) { while (--spec.field_width >= 0) { if (buf < end) *buf = ' '; @@ -1738,29 +1738,21 @@ qualifier: if (spec->qualifier == 'L') spec->type = FORMAT_TYPE_LONG_LONG; else if (spec->qualifier == 'l') { - if (spec->flags & SIGN) - spec->type = FORMAT_TYPE_LONG; - else - spec->type = FORMAT_TYPE_ULONG; + BUILD_BUG_ON(FORMAT_TYPE_ULONG + SIGN != FORMAT_TYPE_LONG); + spec->type = FORMAT_TYPE_ULONG + (spec->flags & SIGN); } else if (_tolower(spec->qualifier) == 'z') { spec->type = FORMAT_TYPE_SIZE_T; } else if (spec->qualifier == 't') { spec->type = FORMAT_TYPE_PTRDIFF; } else if (spec->qualifier == 'H') { - if (spec->flags & SIGN) - spec->type = FORMAT_TYPE_BYTE; - else - spec->type = FORMAT_TYPE_UBYTE; + BUILD_BUG_ON(FORMAT_TYPE_UBYTE + SIGN != FORMAT_TYPE_BYTE); + spec->type = FORMAT_TYPE_UBYTE + (spec->flags & SIGN); } else if (spec->qualifier == 'h') { - if (spec->flags & SIGN) - spec->type = FORMAT_TYPE_SHORT; - else - spec->type = FORMAT_TYPE_USHORT; + BUILD_BUG_ON(FORMAT_TYPE_USHORT + SIGN != FORMAT_TYPE_SHORT); + spec->type = FORMAT_TYPE_USHORT + (spec->flags & SIGN); } else { - if (spec->flags & SIGN) - spec->type = FORMAT_TYPE_INT; - else - spec->type = FORMAT_TYPE_UINT; + BUILD_BUG_ON(FORMAT_TYPE_UINT + SIGN != FORMAT_TYPE_INT); + spec->type = FORMAT_TYPE_UINT + (spec->flags & SIGN); } return ++fmt - start; |