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Subject[PATCH v4 3/3] powerpc/lib: optimise PPC32 memcmp
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Date
At the time being, memcmp() compares two chunks of memory
byte per byte.

This patch optimises the comparison by comparing word by word.

A small benchmark performed on an 8xx comparing two chuncks
of 512 bytes performed 100000 times gives:

Before : 5852274 TB ticks
After: 1488638 TB ticks

This is almost 4 times faster

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
Not resending the entire serie

v4: Dropped the special handling for when length is 0. Handling it
through the small length path.

arch/powerpc/lib/string_32.S | 48
+++++++++++++++++++++++++++++++++++---------
1 file changed, 38 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/lib/string_32.S b/arch/powerpc/lib/string_32.S
index 40a576d56ac7..542e6cecbcaf 100644
--- a/arch/powerpc/lib/string_32.S
+++ b/arch/powerpc/lib/string_32.S
@@ -16,17 +16,45 @@
.text

_GLOBAL(memcmp)
- cmpwi cr0, r5, 0
- beq- 2f
- mtctr r5
- addi r6,r3,-1
- addi r4,r4,-1
-1: lbzu r3,1(r6)
- lbzu r0,1(r4)
- subf. r3,r0,r3
- bdnzt 2,1b
+ srawi. r7, r5, 2 /* Divide len by 4 */
+ mr r6, r3
+ beq- 3f
+ mtctr r7
+ li r7, 0
+1:
+#ifdef __LITTLE_ENDIAN__
+ lwbrx r3, r6, r7
+ lwbrx r0, r4, r7
+#else
+ lwzx r3, r6, r7
+ lwzx r0, r4, r7
+#endif
+ addi r7, r7, 4
+ cmplw cr0, r3, r0
+ bdnzt eq, 1b
+ bne 5f
+3: andi. r3, r5, 3
+ beqlr
+ cmplwi cr1, r3, 2
+ blt- cr1, 4f
+#ifdef __LITTLE_ENDIAN__
+ lhbrx r3, r6, r7
+ lhbrx r0, r4, r7
+#else
+ lhzx r3, r6, r7
+ lhzx r0, r4, r7
+#endif
+ addi r7, r7, 2
+ subf. r3, r0, r3
+ beqlr cr1
+ bnelr
+4: lbzx r3, r6, r7
+ lbzx r0, r4, r7
+ subf. r3, r0, r3
blr
-2: li r3,0
+5: li r3, 1
+ bgtlr
+ li r3, -1
blr
EXPORT_SYMBOL(memcmp)

--
2.13.3
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