linux-kernel - [PATCH] lib/string.c: make strncmp() smaller

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

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 8 Feb 2019 10:34:03 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] lib/string.c: make strncmp() smaller

Space savings on x86_64:

	add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-29 (-29)
	Function                                     old     new   delta
	strncmp                                       67      38     -29

Space savings on arm:

	add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-60 (-60)
	Function                                     old     new   delta
	strncmp                                      116      56     -60

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 lib/string.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/lib/string.c
+++ b/lib/string.c
@@ -344,16 +344,14 @@ EXPORT_SYMBOL(strcmp);
  */
 int strncmp(const char *cs, const char *ct, size_t count)
 {
-	unsigned char c1, c2;
+	while (count--) {
+		unsigned int c1 = *(unsigned char *)cs++;
+		unsigned int c2 = *(unsigned char *)ct++;
 
-	while (count) {
-		c1 = *cs++;
-		c2 = *ct++;
 		if (c1 != c2)
-			return c1 < c2 ? -1 : 1;
+			return c1 - c2;
 		if (!c1)
 			break;
-		count--;
 	}
 	return 0;
 }