CoCalc -- ev67-strrchr.S

GitHub Repository: awilliam/linux-vfio
Path: blob/master/arch/alpha/lib/ev67-strrchr.S
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/*
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 * arch/alpha/lib/ev67-strrchr.S
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 * 21264 version by Rick Gorton <[email protected]>
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 *
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 * Finds length of a 0-terminated string.  Optimized for the
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 * Alpha architecture:
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 *
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 *	- memory accessed as aligned quadwords only
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 *	- uses bcmpge to compare 8 bytes in parallel
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 *
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 * Much of the information about 21264 scheduling/coding comes from:
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 *	Compiler Writer's Guide for the Alpha 21264
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 *	abbreviated as 'CWG' in other comments here
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 *	ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
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 * Scheduling notation:
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 *	E	- either cluster
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 *	U	- upper subcluster; U0 - subcluster U0; U1 - subcluster U1
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 *	L	- lower subcluster; L0 - subcluster L0; L1 - subcluster L1
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 */
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#include <asm/regdef.h>
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	.set noreorder
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	.set noat
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	.align 4
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	.ent strrchr
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	.globl strrchr
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strrchr:
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	.frame sp, 0, ra
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	.prologue 0
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	and	a1, 0xff, t2	# E : 00000000000000ch
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	insbl	a1, 1, t4	# U : 000000000000ch00
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	insbl	a1, 2, t5	# U : 0000000000ch0000
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	ldq_u   t0, 0(a0)	# L : load first quadword Latency=3
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	mov	zero, t6	# E : t6 is last match aligned addr
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	or	t2, t4, a1	# E : 000000000000chch
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	sll	t5, 8, t3	# U : 00000000ch000000
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	mov	zero, t8	# E : t8 is last match byte compare mask
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	andnot  a0, 7, v0	# E : align source addr
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	or	t5, t3, t3	# E : 00000000chch0000
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	sll	a1, 32, t2	# U : 0000chch00000000
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	sll	a1, 48, t4	# U : chch000000000000
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	or	t4, a1, a1	# E : chch00000000chch
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	or	t2, t3, t2	# E : 0000chchchch0000
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	or	a1, t2, a1	# E : chchchchchchchch
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	lda	t5, -1		# E : build garbage mask
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	cmpbge  zero, t0, t1	# E : bits set iff byte == zero
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	mskqh	t5, a0, t4	# E : Complete garbage mask
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	xor	t0, a1, t2	# E : make bytes == c zero
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	cmpbge	zero, t4, t4	# E : bits set iff byte is garbage
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	cmpbge  zero, t2, t3	# E : bits set iff byte == c
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	andnot	t1, t4, t1	# E : clear garbage from null test
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	andnot	t3, t4, t3	# E : clear garbage from char test
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	bne	t1, $eos	# U : did we already hit the terminator?
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	/* Character search main loop */
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$loop:
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	ldq	t0, 8(v0)	# L : load next quadword
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	cmovne	t3, v0, t6	# E : save previous comparisons match
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	nop			#   : Latency=2, extra map slot (keep nop with cmov)
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	nop
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	cmovne	t3, t3, t8	# E : Latency=2, extra map slot
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	nop			#   : keep with cmovne
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	addq	v0, 8, v0	# E :
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	xor	t0, a1, t2	# E :
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	cmpbge	zero, t0, t1	# E : bits set iff byte == zero
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	cmpbge	zero, t2, t3	# E : bits set iff byte == c
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	beq	t1, $loop	# U : if we havnt seen a null, loop
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	nop
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	/* Mask out character matches after terminator */
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$eos:
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	negq	t1, t4		# E : isolate first null byte match
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	and	t1, t4, t4	# E :
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	subq	t4, 1, t5	# E : build a mask of the bytes up to...
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	or	t4, t5, t4	# E : ... and including the null
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	and	t3, t4, t3	# E : mask out char matches after null
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	cmovne	t3, t3, t8	# E : save it, if match found Latency=2, extra map slot
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	nop			#   : Keep with cmovne
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	nop
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	cmovne	t3, v0, t6	# E :
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	nop			#   : Keep with cmovne
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	/* Locate the address of the last matched character */
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	ctlz	t8, t2		# U0 : Latency=3 (0x40 for t8=0)
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	nop
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	cmoveq	t8, 0x3f, t2	# E : Compensate for case when no match is seen
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	nop			# E : hide the cmov latency (2) behind ctlz latency
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	lda	t5, 0x3f($31)	# E :
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	subq	t5, t2, t5	# E : Normalize leading zero count
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	addq	t6, t5, v0	# E : and add to quadword address
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	ret			# L0 : Latency=3
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	nop
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	nop
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	.end strrchr
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