1/*
2 * arch/alpha/lib/ev67-strchr.S
3 * 21264 version contributed by Rick Gorton <rick.gorton@alpha-processor.com>
4 *
5 * Return the address of a given character within a null-terminated
6 * string, or null if it is not found.
7 *
8 * Much of the information about 21264 scheduling/coding comes from:
9 *	Compiler Writer's Guide for the Alpha 21264
10 *	abbreviated as 'CWG' in other comments here
11 *	ftp.digital.com/pub/Digital/info/semiconductor/literature/dsc-library.html
12 * Scheduling notation:
13 *	E	- either cluster
14 *	U	- upper subcluster; U0 - subcluster U0; U1 - subcluster U1
15 *	L	- lower subcluster; L0 - subcluster L0; L1 - subcluster L1
16 * Try not to change the actual algorithm if possible for consistency.
17 */
18
19#include <alpha/regdef.h>
20
21	.set noreorder
22	.set noat
23
24	.align 4
25	.globl strchr
26	.ent strchr
27strchr:
28	.frame sp, 0, ra
29	.prologue 0
30
31	ldq_u   t0, 0(a0)	# L : load first quadword Latency=3
32	and	a1, 0xff, t3	# E : 00000000000000ch
33	insbl	a1, 1, t5	# U : 000000000000ch00
34	insbl	a1, 7, a2	# U : ch00000000000000
35
36	insbl	t3, 6, a3	# U : 00ch000000000000
37	or	t5, t3, a1	# E : 000000000000chch
38	andnot  a0, 7, v0	# E : align our loop pointer
39	lda	t4, -1		# E : build garbage mask
40
41	mskqh	t4, a0, t4	# U : only want relevant part of first quad
42	or	a2, a3, a2	# E : chch000000000000
43	inswl	a1, 2, t5	# E : 00000000chch0000
44	inswl	a1, 4, a3	# E : 0000chch00000000
45
46	or	a1, a2, a1	# E : chch00000000chch
47	or	a3, t5, t5	# E : 0000chchchch0000
48	cmpbge  zero, t0, t2	# E : bits set iff byte == zero
49	cmpbge	zero, t4, t4	# E : bits set iff byte is garbage
50
51	/* This quad is _very_ serialized.  Lots of stalling happens */
52	or	t5, a1, a1	# E : chchchchchchchch
53	xor	t0, a1, t1	# E : make bytes == c zero
54	cmpbge  zero, t1, t3	# E : bits set iff byte == c
55	or	t2, t3, t0	# E : bits set iff char match or zero match
56
57	andnot	t0, t4, t0	# E : clear garbage bits
58	cttz	t0, a2		# U0 : speculative (in case we get a match)
59	nop			# E :
60	bne	t0, $found	# U :
61
62	/*
63	 * Yuk.  This loop is going to stall like crazy waiting for the
64	 * data to be loaded.  Not much can be done about it unless it's
65	 * unrolled multiple times - is that safe to do in kernel space?
66	 * Or would exception handling recovery code do the trick here?
67	 */
68$loop:	ldq	t0, 8(v0)	# L : Latency=3
69	addq	v0, 8, v0	# E :
70	xor	t0, a1, t1	# E :
71	cmpbge	zero, t0, t2	# E : bits set iff byte == 0
72
73	cmpbge	zero, t1, t3	# E : bits set iff byte == c
74	or	t2, t3, t0	# E :
75	cttz	t3, a2		# U0 : speculative (in case we get a match)
76	beq	t0, $loop	# U :
77
78$found:	negq    t0, t1		# E : clear all but least set bit
79	and     t0, t1, t0	# E :
80	and	t0, t3, t1	# E : bit set iff byte was the char
81	addq	v0, a2, v0	# E : Add in the bit number from above
82
83	cmoveq	t1, $31, v0	# E : Two mapping slots, latency = 2
84	nop
85	nop
86	ret			# L0 :
87
88	.end strchr
89