swab.S revision 22993 
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 *	$Id$
31 */
32
33#if defined(LIBC_RCS) && !defined(lint)
34	.text
35	.asciz "$Id$"
36#endif
37
38#include "DEFS.h"
39
40/*
41 * void
42 * swab (const void *src, void *dst, size_t len)
43 *	copy len bytes from src to dst, swapping adjacent bytes
44 *
45 * On the i486, this code is negligibly faster than the code generated
46 * by gcc at about half the size.  If my i386 databook is correct, it
47 * should be considerably faster than the gcc code on a i386.
48 *
49 * Written by:
50 *	J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc.
51 */
52
53ENTRY(swab)
54	pushl	%esi
55	pushl	%edi
56	movl	12(%esp),%esi
57	movl	16(%esp),%edi
58	movl	20(%esp),%ecx
59
60	cld				# set direction forward
61
62	shrl	$1,%ecx
63	testl	$7,%ecx			# copy first group of 1 to 7 words
64	jz	L2			# while swaping alternate bytes.
65	.align	2,0x90
66L1:	lodsw
67	rorw	$8,%ax
68	stosw
69	decl	%ecx
70	testl	$7,%ecx
71	jnz	L1
72
73L2:	shrl	$3,%ecx			# copy remainder 8 words at a time
74	jz	L4			# while swapping alternate bytes.
75	.align	2,0x90
76L3:	lodsw
77	rorw	$8,%ax
78	stosw
79	lodsw
80	rorw	$8,%ax
81	stosw
82	lodsw
83	rorw	$8,%ax
84	stosw
85	lodsw
86	rorw	$8,%ax
87	stosw
88	lodsw
89	rorw	$8,%ax
90	stosw
91	lodsw
92	rorw	$8,%ax
93	stosw
94	lodsw
95	rorw	$8,%ax
96	stosw
97	lodsw
98	rorw	$8,%ax
99	stosw
100	decl	%ecx
101	jnz	L3
102
103L4:	popl	%edi
104	popl	%esi
105	ret
106