swab.S revision 81586 
1/*
2 * Copyright (c) 1993,94 Winning Strategies, Inc.
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 * 3. All advertising materials mentioning features or use of this software
14 *    must display the following acknowledgement:
15 *      This product includes software developed by Winning Strategies, Inc.
16 * 4. The name of the author may not be used to endorse or promote products
17 *    derived from this software without specific prior written permission
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
20 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
21 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
22 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
23 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
24 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
28 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 */
30
31#if defined(LIBC_RCS) && !defined(lint)
32	.text
33	.asciz "$FreeBSD: head/lib/libc/i386/string/swab.S 81586 2001-08-13 14:06:34Z ru $"
34#endif
35
36#include "DEFS.h"
37
38/*
39 * void
40 * swab (const void *src, void *dst, size_t len)
41 *	copy len bytes from src to dst, swapping adjacent bytes
42 *
43 * On the i486, this code is negligibly faster than the code generated
44 * by gcc at about half the size.  If my i386 databook is correct, it
45 * should be considerably faster than the gcc code on a i386.
46 *
47 * Written by:
48 *	J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc.
49 */
50
51ENTRY(swab)
52	pushl	%esi
53	pushl	%edi
54	movl	12(%esp),%esi
55	movl	16(%esp),%edi
56	movl	20(%esp),%ecx
57
58	cld				# set direction forward
59
60	shrl	$1,%ecx
61	testl	$7,%ecx			# copy first group of 1 to 7 words
62	jz	L2			# while swaping alternate bytes.
63	.align	2,0x90
64L1:	lodsw
65	rorw	$8,%ax
66	stosw
67	decl	%ecx
68	testl	$7,%ecx
69	jnz	L1
70
71L2:	shrl	$3,%ecx			# copy remainder 8 words at a time
72	jz	L4			# while swapping alternate bytes.
73	.align	2,0x90
74L3:	lodsw
75	rorw	$8,%ax
76	stosw
77	lodsw
78	rorw	$8,%ax
79	stosw
80	lodsw
81	rorw	$8,%ax
82	stosw
83	lodsw
84	rorw	$8,%ax
85	stosw
86	lodsw
87	rorw	$8,%ax
88	stosw
89	lodsw
90	rorw	$8,%ax
91	stosw
92	lodsw
93	rorw	$8,%ax
94	stosw
95	lodsw
96	rorw	$8,%ax
97	stosw
98	decl	%ecx
99	jnz	L3
100
101L4:	popl	%edi
102	popl	%esi
103	ret
104