ashrdi3.c revision 70949 
1/*-
2 * Copyright (c) 1992, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This software was developed by the Computer Systems Engineering group
6 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
7 * contributed to Berkeley.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 *    notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 *    notice, this list of conditions and the following disclaimer in the
16 *    documentation and/or other materials provided with the distribution.
17 * 3. All advertising materials mentioning features or use of this software
18 *    must display the following acknowledgement:
19 *	This product includes software developed by the University of
20 *	California, Berkeley and its contributors.
21 * 4. Neither the name of the University nor the names of its contributors
22 *    may be used to endorse or promote products derived from this software
23 *    without specific prior written permission.
24 *
25 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
28 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
35 * SUCH DAMAGE.
36 *
37 * $FreeBSD: head/sys/libkern/ashrdi3.c 70949 2001-01-12 07:28:46Z benno $
38 */
39
40#include <libkern/quad.h>
41
42/*
43 * Shift a (signed) quad value right (arithmetic shift right).
44 */
45quad_t
46__ashrdi3(a, shift)
47	quad_t a;
48	qshift_t shift;
49{
50	union uu aa;
51
52	aa.q = a;
53	if (shift >= LONG_BITS) {
54		long s;
55
56		/*
57		 * Smear bits rightward using the machine's right-shift
58		 * method, whether that is sign extension or zero fill,
59		 * to get the `sign word' s.  Note that shifting by
60		 * LONG_BITS is undefined, so we shift (LONG_BITS-1),
61		 * then 1 more, to get our answer.
62		 */
63		s = (aa.sl[H] >> (LONG_BITS - 1)) >> 1;
64		aa.ul[L] = shift >= QUAD_BITS ? s :
65		    aa.sl[H] >> (shift - LONG_BITS);
66		aa.ul[H] = s;
67	} else if (shift > 0) {
68		aa.ul[L] = (aa.ul[L] >> shift) |
69		    (aa.ul[H] << (LONG_BITS - shift));
70		aa.sl[H] >>= shift;
71	}
72	return (aa.q);
73}
74