| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Date: Sat, 21 Feb 2015 00:21:16 +0100
From: Rasmus Villemoes <linux@...musvillemoes.dk>
To: Andrew Morton <akpm@...ux-foundation.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Tejun Heo <tj@...nel.org>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] 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@...musvillemoes.dk>
---
lib/vsprintf.c | 30 +++++++++++-------------------
1 file 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;
--
2.1.3
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists