Module Name: src
Committed By: matt
Date: Sat Dec 29 05:36:57 UTC 2012
Modified Files:
src/common/lib/libc/arch/arm/string: strlen_armv6.S
Log Message:
A few slight speedups (remove one instruction from the main loop).
To generate a diff of this commit:
cvs rdiff -u -r1.1 -r1.2 src/common/lib/libc/arch/arm/string/strlen_armv6.S
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/common/lib/libc/arch/arm/string/strlen_armv6.S
diff -u src/common/lib/libc/arch/arm/string/strlen_armv6.S:1.1 src/common/lib/libc/arch/arm/string/strlen_armv6.S:1.2
--- src/common/lib/libc/arch/arm/string/strlen_armv6.S:1.1 Fri Dec 28 07:10:41 2012
+++ src/common/lib/libc/arch/arm/string/strlen_armv6.S Sat Dec 29 05:36:57 2012
@@ -29,27 +29,27 @@
#include <machine/asm.h>
-RCSID("$NetBSD: strlen_armv6.S,v 1.1 2012/12/28 07:10:41 matt Exp $")
+RCSID("$NetBSD: strlen_armv6.S,v 1.2 2012/12/29 05:36:57 matt Exp $")
.text
ENTRY(strlen)
+ add ip, r0, #4 /* for the final post-inc */
ands r1, r0, #3 /* get misalignment */
- bic ip, r0, #3 /* align to word boundary */
- ldr r3, [ip], #4 /* load first word */
- neg r0, r1 /* subtract misalignment from length */
+ bic r0, r0, #3 /* align to word boundary */
+ ldr r3, [r0], #4 /* load first word */
beq .Lpre_main_loop /* misaligned? no, go to loop */
/*
* For misaligned string, we need to make sure that the bytes before
* the start of the string will not cause a false match to a NUL.
*/
mvn r2, #0 /* create a mask */
- and r1, r0, #3 /* find out how many bytes to clear */
mov r1, r1, lsl #3 /* bytes -> bits */
#ifdef __ARMEL__
- mov r2, r2, lsr r1 /* clear relavent bytes */
-#else
mov r2, r2, lsl r1 /* clear relavent bytes */
+#else
+ mov r2, r2, lsr r1 /* clear relavent bytes */
#endif
+ mvn r2, r2 /* invert mask */
orr r3, r3, r2 /* orr in mask for leading bytes */
.Lpre_main_loop:
#ifdef _ARM_ARCH_7
@@ -68,19 +68,24 @@ ENTRY(strlen)
*/
uqadd8 r3, r3, r1 /* magic happens here */
mvns r3, r3 /* is the complemented result 0? */
- bne .Lreturn /* no, return # of bytes */
- add r0, r0, #4 /* add 4 to the count */
- ldr r3, [ip], #4 /* load next word */
+ bne .Lreturn /* no, then we encountered a NUL */
+ ldr r3, [r0], #4 /* load next word */
b .Lmain_loop /* and go */
-.Lreturn:
/*
* We encountered a NUL. Find out where by doing a CLZ and then
* shifting right by 3. That will be the number of non-NUL bytes.
*/
+.Lreturn:
#ifdef __ARMEL__
rev r3, r3 /* we want this in BE for the CLZ */
#endif
clz r3, r3 /* count how many leading zeros */
add r0, r0, r3, lsr #3 /* divide that by 8 and add to count */
+ /*
+ * r0 now points to 4 past the NUL due to the post-inc. Subtract
+ * the start of the string (which also has 4 added to it to compensate
+ * for the post-inc.
+ */
+ sub r0, r0, ip /* subtract start to get length */
RET
END(strlen)
