The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/libkern/ashrdi3.c

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    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: releng/5.1/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  */
   45 quad_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 }

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