1/* memset/bzero -- set memory area to CH/0
2 Highly optimized version for ix86, x>=5.
3 Copyright (C) 1996-2024 Free Software Foundation, Inc.
4 This file is part of the GNU C Library.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20#include <sysdep.h>
21#include "asm-syntax.h"
22
23#define PARMS 4+4 /* space for 1 saved reg */
24#define RTN PARMS
25#define DEST RTN
26#define CHR DEST+4
27#define LEN CHR+4
28
29 .text
30#if defined SHARED && IS_IN (libc)
31ENTRY (__memset_chk)
32 movl 12(%esp), %eax
33 cmpl %eax, 16(%esp)
34 jb HIDDEN_JUMPTARGET (__chk_fail)
35END (__memset_chk)
36libc_hidden_builtin_def (__memset_chk)
37#endif
38ENTRY (memset)
39
40 pushl %edi
41 cfi_adjust_cfa_offset (4)
42
43 movl DEST(%esp), %edi
44 cfi_rel_offset (edi, 0)
45 movl LEN(%esp), %edx
46 movb CHR(%esp), %al
47 movb %al, %ah
48 movl %eax, %ecx
49 shll $16, %eax
50 movw %cx, %ax
51 cld
52
53/* If less than 36 bytes to write, skip tricky code (it wouldn't work). */
54 cmpl $36, %edx
55 movl %edx, %ecx /* needed when branch is taken! */
56 jl L(2)
57
58/* First write 0-3 bytes to make the pointer 32-bit aligned. */
59 movl %edi, %ecx /* Copy ptr to ecx... */
60 negl %ecx /* ...and negate that and... */
61 andl $3, %ecx /* ...mask to get byte count. */
62 subl %ecx, %edx /* adjust global byte count */
63 rep
64 stosb
65
66 subl $32, %edx /* offset count for unrolled loop */
67 movl (%edi), %ecx /* Fetch destination cache line */
68
69 .align 2, 0x90 /* supply 0x90 for broken assemblers */
70L(1): movl 28(%edi), %ecx /* allocate cache line for destination */
71 subl $32, %edx /* decr loop count */
72 movl %eax, 0(%edi) /* store words pairwise */
73 movl %eax, 4(%edi)
74 movl %eax, 8(%edi)
75 movl %eax, 12(%edi)
76 movl %eax, 16(%edi)
77 movl %eax, 20(%edi)
78 movl %eax, 24(%edi)
79 movl %eax, 28(%edi)
80 leal 32(%edi), %edi /* update destination pointer */
81 jge L(1)
82
83 leal 32(%edx), %ecx /* reset offset count */
84
85/* Write last 0-7 full 32-bit words (up to 8 words if loop was skipped). */
86L(2): shrl $2, %ecx /* convert byte count to longword count */
87 rep
88 stosl
89
90/* Finally write the last 0-3 bytes. */
91 movl %edx, %ecx
92 andl $3, %ecx
93 rep
94 stosb
95
96 /* Load result (only if used as memset). */
97 movl DEST(%esp), %eax /* start address of destination is result */
98 popl %edi
99 cfi_adjust_cfa_offset (-4)
100 cfi_restore (edi)
101
102 ret
103END (memset)
104libc_hidden_builtin_def (memset)
105

source code of glibc/sysdeps/i386/i586/memset.S