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/arch/alpha/lib/ev67-strrchr.S

http://github.com/mirrors/linux
Assembly | 111 lines | 111 code | 0 blank | 0 comment | 1 complexity | 493261a5ee03cffcc1da4cfde6d7d4d9 MD5 | raw file
  1/* SPDX-License-Identifier: GPL-2.0 */
  2/*
  3 * arch/alpha/lib/ev67-strrchr.S
  4 * 21264 version by Rick Gorton <rick.gorton@alpha-processor.com>
  5 *
  6 * Finds length of a 0-terminated string.  Optimized for the
  7 * Alpha architecture:
  8 *
  9 *	- memory accessed as aligned quadwords only
 10 *	- uses bcmpge to compare 8 bytes in parallel
 11 *
 12 * Much of the information about 21264 scheduling/coding comes from:
 13 *	Compiler Writer's Guide for the Alpha 21264
 14 *	abbreviated as 'CWG' in other comments here
 15 *	ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
 16 * Scheduling notation:
 17 *	E	- either cluster
 18 *	U	- upper subcluster; U0 - subcluster U0; U1 - subcluster U1
 19 *	L	- lower subcluster; L0 - subcluster L0; L1 - subcluster L1
 20 */
 21
 22#include <asm/export.h>
 23#include <asm/regdef.h>
 24
 25	.set noreorder
 26	.set noat
 27
 28	.align 4
 29	.ent strrchr
 30	.globl strrchr
 31strrchr:
 32	.frame sp, 0, ra
 33	.prologue 0
 34
 35	and	a1, 0xff, t2	# E : 00000000000000ch
 36	insbl	a1, 1, t4	# U : 000000000000ch00
 37	insbl	a1, 2, t5	# U : 0000000000ch0000
 38	ldq_u   t0, 0(a0)	# L : load first quadword Latency=3
 39
 40	mov	zero, t6	# E : t6 is last match aligned addr
 41	or	t2, t4, a1	# E : 000000000000chch
 42	sll	t5, 8, t3	# U : 00000000ch000000
 43	mov	zero, t8	# E : t8 is last match byte compare mask
 44
 45	andnot  a0, 7, v0	# E : align source addr
 46	or	t5, t3, t3	# E : 00000000chch0000
 47	sll	a1, 32, t2	# U : 0000chch00000000
 48	sll	a1, 48, t4	# U : chch000000000000
 49
 50	or	t4, a1, a1	# E : chch00000000chch
 51	or	t2, t3, t2	# E : 0000chchchch0000
 52	or	a1, t2, a1	# E : chchchchchchchch
 53	lda	t5, -1		# E : build garbage mask
 54
 55	cmpbge  zero, t0, t1	# E : bits set iff byte == zero
 56	mskqh	t5, a0, t4	# E : Complete garbage mask
 57	xor	t0, a1, t2	# E : make bytes == c zero
 58	cmpbge	zero, t4, t4	# E : bits set iff byte is garbage
 59
 60	cmpbge  zero, t2, t3	# E : bits set iff byte == c
 61	andnot	t1, t4, t1	# E : clear garbage from null test
 62	andnot	t3, t4, t3	# E : clear garbage from char test
 63	bne	t1, $eos	# U : did we already hit the terminator?
 64
 65	/* Character search main loop */
 66$loop:
 67	ldq	t0, 8(v0)	# L : load next quadword
 68	cmovne	t3, v0, t6	# E : save previous comparisons match
 69	nop			#   : Latency=2, extra map slot (keep nop with cmov)
 70	nop
 71
 72	cmovne	t3, t3, t8	# E : Latency=2, extra map slot
 73	nop			#   : keep with cmovne
 74	addq	v0, 8, v0	# E :
 75	xor	t0, a1, t2	# E :
 76
 77	cmpbge	zero, t0, t1	# E : bits set iff byte == zero
 78	cmpbge	zero, t2, t3	# E : bits set iff byte == c
 79	beq	t1, $loop	# U : if we havnt seen a null, loop
 80	nop
 81
 82	/* Mask out character matches after terminator */
 83$eos:
 84	negq	t1, t4		# E : isolate first null byte match
 85	and	t1, t4, t4	# E :
 86	subq	t4, 1, t5	# E : build a mask of the bytes up to...
 87	or	t4, t5, t4	# E : ... and including the null
 88
 89	and	t3, t4, t3	# E : mask out char matches after null
 90	cmovne	t3, t3, t8	# E : save it, if match found Latency=2, extra map slot
 91	nop			#   : Keep with cmovne
 92	nop
 93
 94	cmovne	t3, v0, t6	# E :
 95	nop			#   : Keep with cmovne
 96	/* Locate the address of the last matched character */
 97	ctlz	t8, t2		# U0 : Latency=3 (0x40 for t8=0)
 98	nop
 99
100	cmoveq	t8, 0x3f, t2	# E : Compensate for case when no match is seen
101	nop			# E : hide the cmov latency (2) behind ctlz latency
102	lda	t5, 0x3f($31)	# E :
103	subq	t5, t2, t5	# E : Normalize leading zero count
104
105	addq	t6, t5, v0	# E : and add to quadword address
106	ret			# L0 : Latency=3
107	nop
108	nop
109
110	.end strrchr
111	EXPORT_SYMBOL(strrchr)