Subversion Repositories planix.SVN

#include "os.h"

#include <mp.h>

#include "dat.h"

// res = b << shift

void

mpleft(mpint *b, int shift, mpint *res)

{

	int d, l, r, i, otop;

	mpdigit this, last;

	// a negative left shift is a right shift

	if(shift < 0){

		mpright(b, -shift, res);

		return;

	}

	// b and res may be the same so remember the old top

	otop = b->top;

	// shift

	mpbits(res, otop*Dbits + shift);	// overkill

	res->top = DIGITS(otop*Dbits + shift);

	d = shift/Dbits;

	l = shift - d*Dbits;

	r = Dbits - l;

	if(l == 0){

		for(i = otop-1; i >= 0; i--)

			res->p[i+d] = b->p[i];

	} else {

		last = 0;

		for(i = otop-1; i >= 0; i--) {

			this = b->p[i];

			res->p[i+d+1] = (last<<l) | (this>>r);

			last = this;

		}

		res->p[d] = last<<l;

	}

	for(i = 0; i < d; i++)

		res->p[i] = 0;

	// normalize

	while(res->top > 0 && res->p[res->top-1] == 0)

		res->top--;

}