1/* Copyright (C) 1996-2021 Free Software Foundation, Inc.
2   This file is part of the GNU C Library.
3
4   The GNU C Library is free software; you can redistribute it and/or
5   modify it under the terms of the GNU Lesser General Public
6   License as published by the Free Software Foundation; either
7   version 2.1 of the License, or (at your option) any later version.
8
9   The GNU C Library is distributed in the hope that it will be useful,
10   but WITHOUT ANY WARRANTY; without even the implied warranty of
11   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
12   Lesser General Public License for more details.
13
14   You should have received a copy of the GNU Lesser General Public
15   License along with the GNU C Library.  If not, see
16   <https://www.gnu.org/licenses/>.  */
17
18/* Fill a block of memory with zeros.  Optimized for the Alpha architecture:
19
20   - memory accessed as aligned quadwords only
21   - destination memory not read unless needed for good cache behaviour
22   - basic blocks arranged to optimize branch prediction for full-quadword
23     aligned memory blocks.
24   - partial head and tail quadwords constructed with byte-mask instructions
25
26   This is generally scheduled for the EV5 (got to look out for my own
27   interests :-), but with EV4 needs in mind.  There *should* be no more
28   stalls for the EV4 than there are for the EV5.
29*/
30
31
32#include <sysdep.h>
33
34	.set noat
35	.set noreorder
36
37	.text
38	.type	__bzero, @function
39	.globl	__bzero
40	.usepv	__bzero, USEPV_PROF
41
42	cfi_startproc
43
44	/* On entry to this basic block:
45	   t3 == loop counter
46	   t4 == bytes in partial final word
47	   a0 == possibly misaligned destination pointer  */
48
49	.align 3
50bzero_loop:
51	beq	t3, $tail	#
52	blbc	t3, 0f		# skip single store if count even
53
54	stq_u	zero, 0(a0)	# e0    : store one word
55	subq	t3, 1, t3	# .. e1 :
56	addq	a0, 8, a0	# e0    :
57	beq	t3, $tail	# .. e1 :
58
590:	stq_u	zero, 0(a0)	# e0    : store two words
60	subq	t3, 2, t3	# .. e1 :
61	stq_u	zero, 8(a0)	# e0    :
62	addq	a0, 16, a0	# .. e1 :
63	bne	t3, 0b		# e1    :
64
65$tail:	bne	t4, 1f		# is there a tail to do?
66	ret			# no
67
681:	ldq_u	t0, 0(a0)	# yes, load original data
69	mskqh	t0, t4, t0	#
70	stq_u	t0, 0(a0)	#
71	ret			#
72
73__bzero:
74#ifdef PROF
75	ldgp	gp, 0(pv)
76	lda	AT, _mcount
77	jsr	AT, (AT), _mcount
78#endif
79
80	mov	a0, v0		# e0    : move return value in place
81	beq	a1, $done	# .. e1 : early exit for zero-length store
82	and	a0, 7, t1	# e0    :
83	addq	a1, t1, a1	# e1    : add dest misalignment to count
84	srl	a1, 3, t3	# e0    : loop = count >> 3
85	and	a1, 7, t4	# .. e1 : find number of bytes in tail
86	unop			#       :
87	beq	t1, bzero_loop	# e1    : aligned head, jump right in
88
89	ldq_u	t0, 0(a0)	# e0    : load original data to mask into
90	cmpult	a1, 8, t2	# .. e1 : is this a sub-word set?
91	bne	t2, $oneq	# e1    :
92
93	mskql	t0, a0, t0	# e0    : we span words.  finish this partial
94	subq	t3, 1, t3	# e0    :
95	addq	a0, 8, a0	# .. e1 :
96	stq_u	t0, -8(a0)	# e0    :
97	br 	bzero_loop	# .. e1 :
98
99	.align 3
100$oneq:
101	mskql	t0, a0, t2	# e0    :
102	mskqh	t0, a1, t3	# e0    :
103	or	t2, t3, t0	# e1    :
104	stq_u	t0, 0(a0)	# e0    :
105
106$done:	ret
107
108	cfi_endproc
109weak_alias (__bzero, bzero)
110