powerpc32: optimise a few instructions in csum_partial()

r5 does contain the value to be updated, so lets use r5 all way long
for that. It makes the code more readable.

To avoid confusion, it is better to use adde instead of addc

The first addition is useless. Its only purpose is to clear carry.
As r4 is a signed int that is always positive, this can be done by
using srawi instead of srwi

Let's also remove the comment about bdnz having no overhead as it
is not correct on all powerpc, at least on MPC8xx

In the last part, in our situation, the remaining quantity of bytes
to be proceeded is between 0 and 3. Therefore, we can base that part
on the value of bit 31 and bit 30 of r4 instead of anding r4 with 3
then proceding on comparisons and substractions.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <oss@buserror.net>

diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S
index 347237253d1e27f086da948a5ebbbf8be7e93fa1..9c126028ab9c3d7c533aa613f247d2815beb3f30 100644 (file)
--- a/arch/powerpc/lib/checksum_32.S
+++ b/arch/powerpc/lib/checksum_32.S
@@ -27,35 +27,32 @@
  * csum_partial(buff, len, sum)
  */
 _GLOBAL(csum_partial)
-       addic   r0,r5,0
        subi    r3,r3,4
-       srwi.   r6,r4,2
+       srawi.  r6,r4,2         /* Divide len by 4 and also clear carry */
        beq     3f              /* if we're doing < 4 bytes */
-       andi.   r5,r3,2         /* Align buffer to longword boundary */
+       andi.   r0,r3,2         /* Align buffer to longword boundary */
        beq+    1f
-       lhz     r5,4(r3)        /* do 2 bytes to get aligned */
-       addi    r3,r3,2
+       lhz     r0,4(r3)        /* do 2 bytes to get aligned */
        subi    r4,r4,2
-       addc    r0,r0,r5
+       addi    r3,r3,2
        srwi.   r6,r4,2         /* # words to do */
+       adde    r5,r5,r0
        beq     3f
 1:     mtctr   r6
-2:     lwzu    r5,4(r3)        /* the bdnz has zero overhead, so it should */
-       adde    r0,r0,r5        /* be unnecessary to unroll this loop */
+2:     lwzu    r0,4(r3)
+       adde    r5,r5,r0
        bdnz    2b
-       andi.   r4,r4,3
-3:     cmpwi   0,r4,2
-       blt+    4f
-       lhz     r5,4(r3)
+3:     andi.   r0,r4,2
+       beq+    4f
+       lhz     r0,4(r3)
        addi    r3,r3,2
-       subi    r4,r4,2
-       adde    r0,r0,r5
-4:     cmpwi   0,r4,1
-       bne+    5f
-       lbz     r5,4(r3)
-       slwi    r5,r5,8         /* Upper byte of word */
-       adde    r0,r0,r5
-5:     addze   r3,r0           /* add in final carry */
+       adde    r5,r5,r0
+4:     andi.   r0,r4,1
+       beq+    5f
+       lbz     r0,4(r3)
+       slwi    r0,r0,8         /* Upper byte of word */
+       adde    r5,r5,r0
+5:     addze   r3,r5           /* add in final carry */
        blr
 
 /*