libmp/common/mdiv.c

/*  Copyright (c) 1984, 1986, 1987, 1988, 1989 AT&T */
/*    All Rights Reserved   */


/*
 * Copyright (c) 1980 Regents of the University of California.
 * All rights reserved.  The Berkeley software License Agreement
 * specifies the terms and conditions for redistribution.
 */
/*  Portions Copyright(c) 1988, Sun Microsystems Inc.   */
/*  All Rights Reserved                 */

/*
 * Copyright (c) 1997, by Sun Microsystems, Inc.
 * All rights reserved.
 */

#ident  "%Z%%M% %I% %E% SMI"    /* SVr4.0 1.1   */

/* LINTLIBRARY */

#include <mp.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include "libmp.h"

static void m_div(MINT *, MINT *, MINT *, MINT *);

void
mp_mdiv(MINT *a, MINT *b, MINT *q, MINT *r)
{
    MINT x, y;
    int sign;

    sign = 1;
    x.len = y.len = 0;
    _mp_move(a, &x);
    _mp_move(b, &y);
    if (x.len < 0) {
        sign = -1;
        x.len = -x.len;
    }
    if (y.len < 0) {
        sign = -sign;
        y.len = -y.len;
    }
    _mp_xfree(q);
    _mp_xfree(r);
    m_div(&x, &y, q, r);
    if (sign == -1) {
        q->len = -q->len;
        r->len = -r->len;
    }
    _mp_xfree(&x);
    _mp_xfree(&y);
}

static int
m_dsb(int qx, int n, short *a, short *b)
{
    int borrow;
    int s3b2shit;
    int j;
    short fifteen = 15;
    short *aptr, *bptr;
#ifdef DEBUGDSB
    (void) printf("m_dsb %d %d %d %d\n", qx, n, *a, *b);
#endif

    borrow = 0;
    aptr = a;
    bptr = b;
    for (j = n; j > 0; j--) {
#ifdef DEBUGDSB
        (void) printf("1 borrow=%x %d %d %d\n", borrow, (*aptr * qx),
            *bptr, *aptr);
#endif
        borrow -= (*aptr++) * qx - *bptr;
#ifdef DEBUGDSB
        (void) printf("2 borrow=%x %d %d %d\n", borrow, (*aptr * qx),
            *bptr, *aptr);
#endif
        *bptr++ = (short)(borrow & 077777);
#ifdef DEBUGDSB
        (void) printf("3 borrow=%x %d %d %d\n", borrow, (*aptr * qx),
            *bptr, *aptr);
#endif
        if (borrow >= 0) borrow >>= fifteen; /* 3b2 */
        else borrow = 0xfffe0000 | (borrow >> fifteen);
#ifdef DEBUGDSB
        (void) printf("4 borrow=%x %d %d %d\n", borrow, (*aptr * qx),
            *bptr, *aptr);
#endif
    }
    borrow += *bptr;
    *bptr = (short)(borrow & 077777);
        if (borrow >= 0) s3b2shit = borrow >> fifteen; /* 3b2 */
        else s3b2shit = 0xfffe0000 | (borrow >> fifteen);
    if (s3b2shit == 0) {
#ifdef DEBUGDSB
    (void) printf("mdsb 0\n");
#endif
        return (0);
    }
    borrow = 0;
    aptr = a;
    bptr = b;
    for (j = n; j > 0; j--) {
        borrow += *aptr++ + *bptr;
        *bptr++ = (short)(borrow & 077777);
        if (borrow >= 0) borrow >>= fifteen; /* 3b2 */
        else borrow = 0xfffe0000 | (borrow >>fifteen);
    }
#ifdef DEBUGDSB
    (void) printf("mdsb 1\n");
#endif
    return (1);
}

static int
m_trq(short v1, short v2, short u1, short u2, short u3)
{
    short d;
    int x1;
    int c1;

    c1 = u1 * 0100000 + u2;
    if (u1 == v1) {
        d = 077777;
    } else {
        d = (short)(c1 / v1);
    }
    do {
        x1 = c1 - v1 * d;
        x1 = x1 * 0100000 + u3 - v2 * d;
        --d;
    } while (x1 < 0);
#ifdef DEBUGMTRQ
    (void) printf("mtrq %d %d %d %d %d %d\n", v1, v2, u1, u2, u3, (d+1));
#endif
    return ((int)d + 1);
}

static void
m_div(MINT *a, MINT *b, MINT *q, MINT *r)
{
    MINT u, v, x, w;
    short d;
    short *qval;
    short *uval;
    int j;
    int qq;
    int n;
    short v1;
    short v2;

    u.len = v.len = x.len = w.len = 0;
    if (b->len == 0) {
        _mp_fatal("mdiv divide by zero");
        return;
    }
    if (b->len == 1) {
        r->val = _mp_xalloc(1, "m_div1");
        mp_sdiv(a, b->val[0], q, r->val);
        if (r->val[0] == 0) {
            free(r->val);
            r->len = 0;
        } else {
            r->len = 1;
        }
        return;
    }
    if (a -> len < b -> len) {
        q->len = 0;
        r->len = a->len;
        r->val = _mp_xalloc(r->len, "m_div2");
        for (qq = 0; qq < r->len; qq++) {
            r->val[qq] = a->val[qq];
        }
        return;
    }
    x.len = 1;
    x.val = &d;
    n = b->len;
    d = 0100000 / (b->val[n - 1] + 1);
    mp_mult(a, &x, &u); /* subtle: relies on mult allocing extra space */
    mp_mult(b, &x, &v);
#ifdef DEBUG_MDIV
    (void) printf("  u=%s\n", mtox(&u));
    (void) printf("  v=%s\n", mtox(&v));
#endif
    v1 = v.val[n - 1];
    v2 = v.val[n - 2];
    qval = _mp_xalloc(a -> len - n + 1, "m_div3");
    uval = u.val;
    for (j = a->len - n; j >= 0; j--) {
        qq = m_trq(v1, v2, uval[j + n], uval[j + n - 1],
                            uval[j + n - 2]);
        if (m_dsb(qq, n, v.val, uval + j))
            qq -= 1;
        qval[j] = (short)qq;
    }
    x.len = n;
    x.val = u.val;
    _mp_mcan(&x);
#ifdef DEBUG_MDIV
    (void) printf("  x=%s\n", mtox(&x));
    (void) printf("  d(in)=%d\n", (d));
#endif
    mp_sdiv(&x, d, &w, &d);
#ifdef DEBUG_MDIV
    (void) printf("  w=%s\n", mtox(&w));
    (void) printf("  d(out)=%d\n", (d));
#endif
    r->len = w.len;
    r->val = w.val;
    q->val = qval;
    qq = a->len - n + 1;
    if (qq > 0 && qval[qq - 1] == 0)
        qq -= 1;
    q->len = qq;
    if (qq == 0)
        free(qval);
    if (x.len != 0)
        _mp_xfree(&u);
    _mp_xfree(&v);
}