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Annotation of sys/lib/libkern/ashrdi3.c, Revision 1.1

1.1     ! nbrk        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. 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: #if defined(LIBC_SCCS) && !defined(lint)
        !            35: static char rcsid[] = "$OpenBSD: ashrdi3.c,v 1.5 2004/11/28 07:23:41 mickey Exp $";
        !            36: #endif /* LIBC_SCCS and not lint */
        !            37:
        !            38: #include "quad.h"
        !            39:
        !            40: /*
        !            41:  * Shift a (signed) quad value right (arithmetic shift right).
        !            42:  */
        !            43: quad_t
        !            44: __ashrdi3(quad_t a, qshift_t shift)
        !            45: {
        !            46:        union uu aa;
        !            47:
        !            48:        if (shift == 0)
        !            49:                return(a);
        !            50:        aa.q = a;
        !            51:        if (shift >= INT_BITS) {
        !            52:                int s;
        !            53:
        !            54:                /*
        !            55:                 * Smear bits rightward using the machine's right-shift
        !            56:                 * method, whether that is sign extension or zero fill,
        !            57:                 * to get the `sign word' s.  Note that shifting by
        !            58:                 * INT_BITS is undefined, so we shift (INT_BITS-1),
        !            59:                 * then 1 more, to get our answer.
        !            60:                 */
        !            61:                /* LINTED inherits machine dependency */
        !            62:                s = (aa.sl[H] >> (INT_BITS - 1)) >> 1;
        !            63:                /* LINTED inherits machine dependency*/
        !            64:                aa.ul[L] = aa.sl[H] >> (shift - INT_BITS);
        !            65:                aa.ul[H] = s;
        !            66:        } else {
        !            67:                aa.ul[L] = (aa.ul[L] >> shift) |
        !            68:                    (aa.ul[H] << (INT_BITS - shift));
        !            69:                /* LINTED inherits machine dependency */
        !            70:                aa.sl[H] >>= shift;
        !            71:        }
        !            72:        return (aa.q);
        !            73: }