1/* Copy SRC to DEST returning the address of the terminating '\0' in DEST.
2   For Intel 80x86, x>=3.
3   Copyright (C) 1994-2021 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/* This function is defined neither in ANSI nor POSIX standards but is
21   also not invented here.  */
22
23#include <sysdep.h>
24#include "asm-syntax.h"
25
26#define PARMS	4		/* no space for saved regs */
27#define RTN	PARMS
28#define DEST	RTN
29#define SRC	DEST+4
30
31	.text
32ENTRY (__stpcpy)
33
34	movl DEST(%esp), %eax
35	movl SRC(%esp), %ecx
36	subl %eax, %ecx		/* magic: reduce number of loop variants
37				   to one using addressing mode */
38
39	/* Here we would like to write
40
41	subl $4, %eax
42	ALIGN (4)
43
44	but the assembler is too smart and optimizes for the shortest
45	form where the number only needs one byte.  But if we could
46	have the long form we would not need the alignment.  */
47
48	.byte 0x81, 0xe8	/* This is `subl $0x00000004, %eax' */
49	.long 0x00000004
50
51	/* Four times unfolded loop with only one loop counter.  This
52	   is achieved by the use of index+base addressing mode.  As the
53	   loop counter we use the destination address because this is
54	   also the result.  */
55L(1):	addl $4, %eax		/* increment loop counter */
56
57	movb (%eax,%ecx), %dl	/* load current char */
58	movb %dl, (%eax)	/* and store it */
59	testb %dl, %dl		/* was it NUL? */
60	jz L(2)			/* yes, then exit */
61
62	movb 1(%eax,%ecx), %dl	/* load current char */
63	movb %dl, 1(%eax)	/* and store it */
64	testb %dl, %dl		/* was it NUL? */
65	jz L(3)			/* yes, then exit */
66
67	movb 2(%eax,%ecx), %dl	/* load current char */
68	movb %dl, 2(%eax)	/* and store it */
69	testb %dl, %dl		/* was it NUL? */
70	jz L(4)			/* yes, then exit */
71
72	movb 3(%eax,%ecx), %dl	/* load current char */
73	movb %dl, 3(%eax)	/* and store it */
74	testb %dl, %dl		/* was it NUL? */
75	jnz L(1)		/* no, then continue loop */
76
77	incl %eax		/* correct loop counter */
78L(4):	incl %eax
79L(3):	incl %eax
80L(2):
81
82	ret
83END (__stpcpy)
84
85weak_alias (__stpcpy, stpcpy)
86libc_hidden_def (__stpcpy)
87libc_hidden_builtin_def (stpcpy)
88