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  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:	Thu, 19 Mar 2015 22:44:41 +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] lib/vsprintf.c: improve put_dec_trunc8 slightly

I hadn't had enough coffee when I wrote this. Currently, the final
increment of buf depends on the value loaded from the table, and
causes gcc to emit a cmov immediately before the return. It is smarter
to let it depend on r, since the increment can then be computed in
parallel with the final load/store pair. It also shaves 16 bytes of
.text.

Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
---
 lib/vsprintf.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index e0bea9e5bbbf..7078d90c187b 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -164,9 +164,9 @@ static const u16 decpair[100] = {
 
 /*
  * This will print a single '0' even if r == 0, since we would
- * immediately jump to out_r where two 0s would be written and one of
- * them then discarded. This is needed by ip4_string below. All other
- * callers pass a non-zero value of r.
+ * immediately jump to out_r where two 0s would be written but only
+ * one of them accounted for in buf. This is needed by ip4_string
+ * below. All other callers pass a non-zero value of r.
 */
 static noinline_for_stack
 char *put_dec_trunc8(char *buf, unsigned r)
@@ -205,9 +205,7 @@ out_q:
 out_r:
 	/* 1 <= r < 100 */
 	*((u16 *)buf) = decpair[r];
-	buf += 2;
-	if (buf[-1] == '0')
-		buf--;
+	buf += r < 10 ? 1 : 2;
 	return buf;
 }
 
-- 
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