Subversion Repositories planix.SVN

#include "os.h"
#include <mp.h>
#include "dat.h"

// res = b >> shift
void
mpright(mpint *b, int shift, mpint *res)
{
        int d, l, r, i;
        mpdigit this, last;

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

        // a negative right shift is a left shift
        if(shift < 0){
                mpleft(b, -shift, res);
                return;
        }

        if(res != b)
                mpbits(res, b->top*Dbits - shift);
        else if(shift == 0)
                return;

        d = shift/Dbits;
        r = shift - d*Dbits;
        l = Dbits - r;

        //  shift all the bits out == zero
        if(d>=b->top){
                res->sign = 1;
                res->top = 0;
                return;
        }

        // special case digit shifts
        if(r == 0){
                for(i = 0; i < b->top-d; i++)
                        res->p[i] = b->p[i+d];
        } else {
                last = b->p[d];
                for(i = 0; i < b->top-d-1; i++){
                        this = b->p[i+d+1];
                        res->p[i] = (this<<l) | (last>>r);
                        last = this;
                }
                res->p[i++] = last>>r;
        }

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