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source/com/hurlant/math/BarrettReduction.as

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+package com.hurlant.math
+{
+	use namespace bi_internal;
+
+	internal class BarrettReduction implements IReduction
+	{
+		private var m:BigInteger;
+		private var r2:BigInteger;
+		private var q3:BigInteger;
+		private var mu:BigInteger;
+		
+		public function BarrettReduction(m:BigInteger) {
+			// setup Barrett
+			r2 = new BigInteger;
+			q3 = new BigInteger;
+			BigInteger.ONE.dlShiftTo(2*m.t, r2);
+			mu = r2.divide(m);
+			this.m = m;
+		}
+		
+		public function revert(x:BigInteger):BigInteger
+		{
+			return x;
+		}
+		
+		/**
+		 * 
+		 * @param x
+		 * @param y
+		 * @param r = x*y mod m; x != r
+		 * 
+		 */
+		public function mulTo(x:BigInteger, y:BigInteger, r:BigInteger):void
+		{
+			x.multiplyTo(y, r);
+			reduce(r);
+		}
+		
+		/**
+		 * 
+		 * @param x
+		 * @param r = x^2 mod m; x != r
+		 * 
+		 */
+		public function sqrTo(x:BigInteger, r:BigInteger):void
+		{
+			x.squareTo(r);
+			reduce(r);
+		}
+		
+		public function convert(x:BigInteger):BigInteger
+		{
+			if (x.s<0 || x.t>2*m.t) {
+				return x.mod(m);
+			} else if (x.compareTo(m)<0) {
+				return x;
+			} else {
+				var r:BigInteger = new BigInteger;
+				x.copyTo(r);
+				reduce(r);
+				return r;
+			}
+		}
+		
+		/**
+		 * 
+		 * @param x = x mod m (HAC 14.42)
+		 * 
+		 */
+		public function reduce(lx:BigInteger):void
+		{
+			var x:BigInteger = lx as BigInteger;
+			x.drShiftTo(m.t-1,r2);
+			if (x.t>m.t+1) {
+				x.t = m.t+1;
+				x.clamp();
+			}
+			mu.multiplyUpperTo(r2, m.t+1, q3);
+			m.multiplyLowerTo(q3, m.t+1, r2);
+			while (x.compareTo(r2)<0) {
+				x.dAddOffset(1, m.t+1);
+			}
+			x.subTo(r2,x);
+			while (x.compareTo(m)>=0) {
+				x.subTo(m,x);
+			}
+		}
+		
+	}
+}