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#include "mprec.h"
#include <assert.h>


/*
 *	Msma takes the mint pointed to by "to" and adds to it (in place)
 *	the product of the following :
 *		1. the mint pointed to by "from".
 *		2. the int "fac" (it is assumed that 0 <= fac < 2 * BASE).
 *		3. BASE raised to the "shift" power.
 *	Note that it is assumed that the length of "to" is big enough to
 *	hold the result.
 *	It is also assumed that "from" and "to" are distinct.
 */

void
msma(from, fac, shift, to)
mint *from, *to;
int fac;
unsigned shift;
{
	register int carry;
	register char *fp, *tp;
	register unsigned count;
	int mifl;

	assert(0 <= fac && fac < 2 * BASE);

	/* general case needs fac != 0, so handle fac == 0 */
	if (fac == 0)
		return;

	/* find out sign of "from" */
	mifl = ispos(from);

	/* do the multiply assuming "from" is positive */
	fp = from->val;
	tp = to->val + shift;
	carry = 0;
	count = from->len;
	if (!mifl)
		--count;
	assert(tp + count <= to->val + to->len);
	while (count-- != 0) {
		carry += *tp + *fp++ * fac;
		*tp++ = carry % BASE;
		carry >>= L2BASE;
	}

	/* propogate carry or borrow */
	count = to->val + to->len - tp;
	if (!mifl)
		carry -= fac;
	while (count-- != 0 && carry != 0) {
		carry += *tp + BASE;
		*tp++ = carry % BASE;
		carry = (carry >> L2BASE) - 1;
	}
}

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