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Annotation of sys/lib/libkern/ashrdi3.c, Revision 1.1.1.1

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: }