src/libthread/Linux-power-asm.s - plan9 - Git at Google

 	.globl	_tas
 _tas:
 	li	%r0, 0
 	mr	%r4, %r3
 	lis	%r5, 0xcafe
 	ori	%r5, %r5, 0xbabe
 1:
 	lwarx	%r3, %r0, %r4
 	cmpwi	%r3, 0
 	bne	2f
 	stwcx.	%r5, %r0, %r4
 	bne-	1b
 2:
 	sync
 	blr
	.globl _tas
	_tas:
	li %r0, 0
	mr %r4, %r3
	lis %r5, 0xcafe
	ori %r5, %r5, 0xbabe
	1:
	lwarx %r3, %r0, %r4
	cmpwi %r3, 0
	bne 2f
	stwcx. %r5, %r0, %r4
	bne- 1b
	2:
	sync
	blr