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 a character. Optimized for the Alpha
19 architecture:
20
21 - memory accessed as aligned quadwords only
22 - destination memory not read unless needed for good cache behaviour
23 - basic blocks arranged to optimize branch prediction for full-quadword
24 aligned memory blocks.
25 - partial head and tail quadwords constructed with byte-mask instructions
26
27 This is generally scheduled for the EV5 (got to look out for my own
28 interests :-), but with EV4 needs in mind. There *should* be no more
29 stalls for the EV4 than there are for the EV5.
30*/
31
32
33#include <sysdep.h>
34
35 .set noat
36 .set noreorder
37
38 .text
39 .type memset, @function
40 .globl memset
41 .usepv memset, USEPV_PROF
42
43 cfi_startproc
44
45 /* On entry to this basic block:
46 t3 == loop counter
47 t4 == bytes in partial final word
48 a0 == possibly misaligned destination pointer
49 a1 == replicated source character */
50
51 .align 3
52memset_loop:
53 beq t3, $tail
54 blbc t3, 0f # skip single store if count even
55
56 stq_u a1, 0(a0) # e0 : store one word
57 subq t3, 1, t3 # .. e1 :
58 addq a0, 8, a0 # e0 :
59 beq t3, $tail # .. e1 :
60
610: stq_u a1, 0(a0) # e0 : store two words
62 subq t3, 2, t3 # .. e1 :
63 stq_u a1, 8(a0) # e0 :
64 addq a0, 16, a0 # .. e1 :
65 bne t3, 0b # e1 :
66
67$tail: bne t4, 1f # is there a tail to do?
68 ret # no
69
70 .align 3
711: ldq_u t0, 0(a0) # e1 : yes, load original data
72 mskql a1, t4, t1 # .. e0 :
73 mskqh t0, t4, t0 # e0 :
74 or t0, t1, t0 # e1 (stall)
75 stq_u t0, 0(a0) # e0 :
76 ret # .. e1 :
77
78memset:
79#ifdef PROF
80 ldgp gp, 0(pv)
81 lda AT, _mcount
82 jsr AT, (AT), _mcount
83#endif
84
85 and a1, 0xff, a1 # e0 : zero extend input character
86 mov a0, v0 # .. e1 : move return value in place
87 sll a1, 8, t0 # e0 : begin replicating the char
88 beq a2, $done # .. e1 : early exit for zero-length store
89 or t0, a1, a1 # e0 :
90 and a0, 7, t1 # .. e1 : dest misalignment
91 sll a1, 16, t0 # e0 :
92 addq a2, t1, a2 # .. e1 : add dest misalignment to count
93 or t0, a1, a1 # e0 :
94 srl a2, 3, t3 # .. e1 : loop = count >> 3
95 sll a1, 32, t0 # e0 :
96 and a2, 7, t4 # .. e1 : find number of bytes in tail
97 or t0, a1, a1 # e0 : character replication done
98
99 beq t1, memset_loop # .. e1 : aligned head, jump right in
100
101 ldq_u t0, 0(a0) # e1 : load original data to mask into
102 mskqh a1, a0, t1 # .. e0 :
103
104 cmpult a2, 8, t2 # e0 : is this a sub-word set?
105 bne t2, $oneq # .. e1 (zdb)
106
107 mskql t0, a0, t0 # e0 : we span words. finish this partial
108 subq t3, 1, t3 # .. e1 :
109 addq a0, 8, a0 # e0 :
110 or t0, t1, t0 # .. e1 :
111 stq_u t0, -8(a0) # e0 :
112 br memset_loop # .. e1 :
113
114 .align 3
115$oneq:
116 mskql t1, a2, t1 # e0 : entire operation within one word
117 mskql t0, a0, t2 # e0 :
118 mskqh t0, a2, t3 # e0 :
119 or t1, t2, t0 # .. e1 :
120 or t0, t3, t0 # e1 :
121 stq_u t0, 0(a0) # e0 (stall)
122
123$done: ret
124
125 cfi_endproc
126libc_hidden_builtin_def (memset)
127

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