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  * 4. Neither the name of the University nor the names of its contributors
   18  *    may be used to endorse or promote products derived from this software
   19  *    without specific prior written permission.
   20  *
   21  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   31  * SUCH DAMAGE.
   32  */
   33 
   34 #include <sys/cdefs.h>
   35 __FBSDID("$FreeBSD: releng/11.2/sys/libkern/ashrdi3.c 331722 2018-03-29 02:50:57Z eadler $");
   36 
   37 #include <libkern/quad.h>
   38 
   39 /*
   40  * Shift a (signed) quad value right (arithmetic shift right).
   41  */
   42 quad_t
   43 __ashrdi3(a, shift)
   44         quad_t a;
   45         qshift_t shift;
   46 {
   47         union uu aa;
   48 
   49         aa.q = a;
   50         if (shift >= LONG_BITS) {
   51                 long s;
   52 
   53                 /*
   54                  * Smear bits rightward using the machine's right-shift
   55                  * method, whether that is sign extension or zero fill,
   56                  * to get the `sign word' s.  Note that shifting by
   57                  * LONG_BITS is undefined, so we shift (LONG_BITS-1),
   58                  * then 1 more, to get our answer.
   59                  */
   60                 s = (aa.sl[H] >> (LONG_BITS - 1)) >> 1;
   61                 aa.ul[L] = shift >= QUAD_BITS ? s :
   62                     aa.sl[H] >> (shift - LONG_BITS);
   63                 aa.ul[H] = s;
   64         } else if (shift > 0) {
   65                 aa.ul[L] = (aa.ul[L] >> shift) |
   66                     (aa.ul[H] << (LONG_BITS - shift));
   67                 aa.sl[H] >>= shift;
   68         }
   69         return (aa.q);
   70 }

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