package com.hurlant.math
{
    use namespace bi_internal;
    /**
     * Montgomery reduction
     */
    internal class MontgomeryReduction implements IReduction
    {
        private var m:BigInteger;
        private var mp:int;
        private var mpl:int;
        private var mph:int;
        private var um:int;
        private var mt2:int;
        public function MontgomeryReduction(m:BigInteger) {
            this.m = m;
            mp = m.invDigit();
            mpl = mp & 0x7fff;
            mph = mp>>15;
            um = (1<<(BigInteger.DB-15))-1;
            mt2 = 2*m.t;
        }
        /**
         * xR mod m
         */
        public function convert(x:BigInteger):BigInteger {
            var r:BigInteger = new BigInteger;
             x.abs().dlShiftTo(m.t, r);
             r.divRemTo(m, null, r);
             if (x.s<0 && r.compareTo(BigInteger.ZERO)>0) {
                 m.subTo(r,r);
             }
             return r;
        }
        /**
         * x/R mod m
         */
        public function revert(x:BigInteger):BigInteger {
            var r:BigInteger = new BigInteger;
            x.copyTo(r);
            reduce(r);
            return r;
        }
        /**
         * x = x/R mod m (HAC 14.32)
         */
        public function reduce(x:BigInteger):void {
            while (x.t<=mt2) {        // pad x so am has enough room later
                x.a[x.t++] = 0;
            }
            for (var i:int=0; i<m.t; ++i) {
                // faster way of calculating u0 = x[i]*mp mod DV
                var j:int = x.a[i]&0x7fff;
                var u0:int = (j*mpl+(((j*mph+(x.a[i]>>15)*mpl)&um)<<15))&BigInteger.DM;
                // use am to combine the multiply-shift-add into one call
                j = i+m.t;
                x.a[j] += m.am(0, u0, x, i, 0, m.t);
                // propagate carry
                while (x.a[j]>=BigInteger.DV) {
                    x.a[j] -= BigInteger.DV;
                    x.a[++j]++;
                }
            }
             x.clamp();
             x.drShiftTo(m.t, x);
             if (x.compareTo(m)>=0) {
                 x.subTo(m,x);
             }
        }
        /**
         * r = "x^2/R mod m"; x != r
         */
        public function sqrTo(x:BigInteger, r:BigInteger):void {
            x.squareTo(r);
            reduce(r);
        }
        /**
         * r = "xy/R mod m"; x,y != r
         */
        public function mulTo(x:BigInteger, y:BigInteger, r:BigInteger):void {
            x.multiplyTo(y,r);
            reduce(r);
        }
    }
}