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;

        res->sign = b->sign;
        if(b->top==0){
                res->top = 0;
                return;
        }

        // a zero or 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;

        res->flags |= b->flags & MPtimesafe;
        mpnorm(res);
}