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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 bits, len;
    struct pbn *d;
    int i, j;
    pbn_atom_t x1;
    pbn_2atom_t c;
    
    bits = s1->bits + s2->bits;
    len = (bits+PBN_ATOM_BITS-1)/PBN_ATOM_BITS;
    
    d = pbn_new(len);
    d->bits = bits;

    for (i = 0; i < s1->len; i++) {
	x1 = s1->num[i];
	c = 0;
	for (j = 0; j < s2->len; j++) {
	    c += (pbn_2atom_t)x1 * s2->num[j];
	    d->num[i+j] += (pbn_atom_t)c;
	    c >>= PBN_ATOM_BITS;
	}
	if (c)
	    d->num[i+j] += (pbn_atom_t)c;
    }
    d->minus = s1->minus ^ s2->minus;

    pbn_free(s1);
    pbn_free(s2);

    _pbn_adjust_bits(d);

    return d;
}