jslong.c

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Mozilla Communicator client code, released
 * March 31, 1998.
 *
 * The Initial Developer of the Original Code is
 * Netscape Communications Corporation.
 * Portions created by the Initial Developer are Copyright (C) 1998
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
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#include "jsstddef.h"
#include "jstypes.h"
#include "jslong.h"

#ifndef JS_HAVE_LONG_LONG
/*
** Divide 64-bit a by 32-bit b, which must be normalized so its high bit is 1.
*/
static void norm_udivmod32(JSUint32 *qp, JSUint32 *rp, JSUint64 a, JSUint32 b)
{
    JSUint32 d1, d0, q1, q0;
    JSUint32 r1, r0, m;

    d1 = jshi16(b);
    d0 = jslo16(b);
    r1 = a.hi % d1;
    q1 = a.hi / d1;
    m = q1 * d0;
    r1 = (r1 << 16) | jshi16(a.lo);
    if (r1 < m) {
        q1--, r1 += b;
        if (r1 >= b     /* i.e., we didn't get a carry when adding to r1 */
            && r1 < m) {
            q1--, r1 += b;
        }
    }
    r1 -= m;
    r0 = r1 % d1;
    q0 = r1 / d1;
    m = q0 * d0;
    r0 = (r0 << 16) | jslo16(a.lo);
    if (r0 < m) {
        q0--, r0 += b;
        if (r0 >= b
            && r0 < m) {
            q0--, r0 += b;
        }
    }
    *qp = (q1 << 16) | q0;
    *rp = r0 - m;
}

static JSUint32 CountLeadingZeros(JSUint32 a)
{
    JSUint32 t;
    JSUint32 r = 32;

    if ((t = a >> 16) != 0)
        r -= 16, a = t;
    if ((t = a >> 8) != 0)
        r -= 8, a = t;
    if ((t = a >> 4) != 0)
        r -= 4, a = t;
    if ((t = a >> 2) != 0)
        r -= 2, a = t;
    if ((t = a >> 1) != 0)
        r -= 1, a = t;
    if (a & 1)
        r--;
    return r;
}

JS_PUBLIC_API(void) jsll_udivmod(JSUint64 *qp, JSUint64 *rp, JSUint64 a, JSUint64 b)
{
    JSUint32 n0, n1, n2;
    JSUint32 q0, q1;
    JSUint32 rsh, lsh;

    n0 = a.lo;
    n1 = a.hi;

    if (b.hi == 0) {
        if (b.lo > n1) {
            /* (0 q0) = (n1 n0) / (0 D0) */

            lsh = CountLeadingZeros(b.lo);

            if (lsh) {
                /*
                 * Normalize, i.e. make the most significant bit of the
                 * denominator be set.
                 */
                b.lo = b.lo << lsh;
                n1 = (n1 << lsh) | (n0 >> (32 - lsh));
                n0 = n0 << lsh;
            }

            a.lo = n0, a.hi = n1;
            norm_udivmod32(&q0, &n0, a, b.lo);
            q1 = 0;

            /* remainder is in n0 >> lsh */
        } else {
            /* (q1 q0) = (n1 n0) / (0 d0) */

            if (b.lo == 0)              /* user wants to divide by zero! */
                b.lo = 1 / b.lo;        /* so go ahead and crash */

            lsh = CountLeadingZeros(b.lo);

            if (lsh == 0) {
                /*
                 * From (n1 >= b.lo)
                 *   && (the most significant bit of b.lo is set),
                 * conclude that
                 *      (the most significant bit of n1 is set)
                 *   && (the leading quotient digit q1 = 1).
                 *
                 * This special case is necessary, not an optimization
                 * (Shifts counts of 32 are undefined).
                 */
                n1 -= b.lo;
                q1 = 1;
            } else {
                /*
                 * Normalize.
                 */
                rsh = 32 - lsh;

                b.lo = b.lo << lsh;
                n2 = n1 >> rsh;
                n1 = (n1 << lsh) | (n0 >> rsh);
                n0 = n0 << lsh;

                a.lo = n1, a.hi = n2;
                norm_udivmod32(&q1, &n1, a, b.lo);
            }

            /* n1 != b.lo... */

            a.lo = n0, a.hi = n1;
            norm_udivmod32(&q0, &n0, a, b.lo);

            /* remainder in n0 >> lsh */
        }

        if (rp) {
            rp->lo = n0 >> lsh;
            rp->hi = 0;
        }
    } else {
        if (b.hi > n1) {
            /* (0 0) = (n1 n0) / (D1 d0) */

            q0 = 0;
            q1 = 0;

            /* remainder in (n1 n0) */
            if (rp) {
                rp->lo = n0;
                rp->hi = n1;
            }
        } else {
            /* (0 q0) = (n1 n0) / (d1 d0) */

            lsh = CountLeadingZeros(b.hi);
            if (lsh == 0) {
                /*
                 * From (n1 >= b.hi)
                 *   && (the most significant bit of b.hi is set),
                 * conclude that
                 *      (the most significant bit of n1 is set)
                 *   && (the quotient digit q0 = 0 or 1).
                 *
                 * This special case is necessary, not an optimization.
                 */

                /*
                 * The condition on the next line takes advantage of that
                 * n1 >= b.hi (true due to control flow).
                 */
                if (n1 > b.hi || n0 >= b.lo) {
                    q0 = 1;
                    a.lo = n0, a.hi = n1;
                    JSLL_SUB(a, a, b);
                } else {
                    q0 = 0;
                }
                q1 = 0;

                if (rp) {
                    rp->lo = n0;
                    rp->hi = n1;
                }
            } else {
                JSInt64 m;

                /*
                 * Normalize.
                 */
                rsh = 32 - lsh;

                b.hi = (b.hi << lsh) | (b.lo >> rsh);
                b.lo = b.lo << lsh;
                n2 = n1 >> rsh;
                n1 = (n1 << lsh) | (n0 >> rsh);
                n0 = n0 << lsh;

                a.lo = n1, a.hi = n2;
                norm_udivmod32(&q0, &n1, a, b.hi);
                JSLL_MUL32(m, q0, b.lo);

                if ((m.hi > n1) || ((m.hi == n1) && (m.lo > n0))) {
                    q0--;
                    JSLL_SUB(m, m, b);
                }

                q1 = 0;

                /* Remainder is ((n1 n0) - (m1 m0)) >> lsh */
                if (rp) {
                    a.lo = n0, a.hi = n1;
                    JSLL_SUB(a, a, m);
                    rp->lo = (a.hi << rsh) | (a.lo >> lsh);
                    rp->hi = a.hi >> lsh;
                }
            }
        }
    }

    if (qp) {
        qp->lo = q0;
        qp->hi = q1;
    }
}
#endif /* !JS_HAVE_LONG_LONG */