Commit 51be17df authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Linus Torvalds
Browse files

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: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7b1460ec

lib/vsprintf.c

+11 −19
Original line number Diff line number Diff line
@@ -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;

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