sys/libkern/ashrdi3.c

   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: src/sys/libkern/ashrdi3.c,v 1.6 1999/08/28 00:46:31 peter Exp $
  38  * $DragonFly: src/sys/libkern/ashrdi3.c,v 1.3 2004/01/26 11:09:44 joerg Exp $
  39  */
  40
  41 #include "quad.h"
  42
  43 /*
  44  * Shift a (signed) quad value right (arithmetic shift right).
  45  */
  46 quad_t
  47 __ashrdi3(quad_t a, qshift_t shift)
  48 {
  49         union uu aa;
  50
  51         aa.q = a;
  52         if (shift >= LONG_BITS) {
  53                 long s;
  54
  55                 /*
  56                  * Smear bits rightward using the machine's right-shift
  57                  * method, whether that is sign extension or zero fill,
  58                  * to get the `sign word' s.  Note that shifting by
  59                  * LONG_BITS is undefined, so we shift (LONG_BITS-1),
  60                  * then 1 more, to get our answer.
  61                  */
  62                 s = (aa.sl[H] >> (LONG_BITS - 1)) >> 1;
  63                 aa.ul[L] = shift >= QUAD_BITS ? s :
  64                     aa.sl[H] >> (shift - LONG_BITS);
  65                 aa.ul[H] = s;
  66         } else if (shift > 0) {
  67                 aa.ul[L] = (aa.ul[L] >> shift) |
  68                     (aa.ul[H] << (LONG_BITS - shift));
  69                 aa.sl[H] >>= shift;
  70         }
  71         return (aa.q);
  72 }