1/* Copyright (C) 1996-2022 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

source code of glibc/sysdeps/alpha/bzero.S