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/* ----------------------------------------------------------------------- *
 *
 *   Copyright 2007 H. Peter Anvin - All Rights Reserved
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Lesser General Public License as
 *   published by the Free Software Foundation, Inc.,
 *   59 Temple Place Ste 330, Boston MA 02111-1307, USA; version 2.1,
 *   incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * pbn_mul.c
 *
 * Multiply two numbers.  This could be made significantly faster for
 * very large numbers by using Karatsuba or FFT-based multiplication.
 */

#include "pbnint.h"

struct pbn *pbn_mul(struct pbn *s1, struct pbn *s2)
{
    size_t i, j, imax, jmax;
    struct pbn *d;
    pbn_limb_t *dp;
    const pbn_limb_t *s2p;
    pbn_limb_t x1;
    pbn_2limb_t t;
    pbn_limb_t c;

    if (s1->bits == 0) {
	pbn_free(s2);
	return s1;		/* s1 == 0 */
    } else if (s2->bits == 0) {
	pbn_free(s1);
	return s2;		/* s2 == 0 */
    }

    imax = (s1->bits+PBN_LIMB_BITS-1) >> PBN_LIMB_SHIFT;
    jmax = (s2->bits+PBN_LIMB_BITS-1) >> PBN_LIMB_SHIFT;

    d = pbn_new(imax+jmax);

    for (i = 0; i < imax; i++) {
	x1 = s1->num[i];
	c = 0;
        s2p = s2->num;
        dp  = &d->num[i];
	for (j = 0; j < jmax; j++) {
	    t = (pbn_2limb_t)x1 * (*s2p++) + *dp + c;
            *dp++ = (pbn_limb_t)t;
            c = t >> PBN_LIMB_BITS;
	}
        *dp = c;
    }
    d->minus = s1->minus ^ s2->minus;

    pbn_free(s1);
    pbn_free(s2);

    return pbn_adjust_bits(d);
}