FreeBSD/Linux Kernel Cross Reference
sys/libkern/subdi3.c

     /*-
      * Copyright (c) 1992, 1993
      *      The Regents of the University of California.  All rights reserved.
      *
      * This software was developed by the Computer Systems Engineering group
      * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
      * contributed to Berkeley.
      *
      * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     * $FreeBSD: src/sys/libkern/subdi3.c,v 1.5 1999/08/28 00:46:38 peter Exp $
     * $DragonFly: src/sys/libkern/subdi3.c,v 1.3 2004/01/26 11:09:44 joerg Exp $
     */
    
    #include "quad.h"
    
    /*
     * Subtract two quad values.  This is trivial since a one-bit carry
     * from a single u_long difference x-y occurs if and only if (x-y) > x.
     */
    quad_t
    __subdi3(quad_t a, quad_t b)
    {
            union uu aa, bb, diff;
    
            aa.q = a;
            bb.q = b;
            diff.ul[L] = aa.ul[L] - bb.ul[L];
            diff.ul[H] = aa.ul[H] - bb.ul[H] - (diff.ul[L] > aa.ul[L]);
            return (diff.q);
    }

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