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 <linux/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)
112