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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>
This commit is contained in:
Rasmus Villemoes 2015-04-15 16:17:02 -07:00 committed by Linus Torvalds
parent 7b1460ecca
commit 51be17dfff
1 changed files with 11 additions and 19 deletions
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30
lib/vsprintf.c
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@ -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 @@ int format_decode(const char *fmt, struct printf_spec *spec)
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;