powerpc32: optimise a few instructions in csum_partial() (48821a34) · Commits · 戴 / test

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>

arch/powerpc/lib/checksum_32.S

+17 −20

Original line number	Diff line number	Diff line
		@@ -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

		/*

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