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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>
This commit is contained in:
Christophe Leroy 2015-09-22 16:34:29 +02:00 committed by Scott Wood
parent 7aef413656
commit 48821a34b1
1 changed files with 17 additions and 20 deletions
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37
arch/powerpc/lib/checksum_32.S
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@ -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
/*