js/DBIG.js

/*
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements.  See the NOTICE file
distributed with this work for additional information
regarding copyright ownership.  The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License.  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied.  See the License for the
specific language governing permissions and limitations
under the License.
*/

/* AMCL double length DBIG number class */

/* constructor */
var DBIG = function(x) {
	this.w=[];
	this.zero();
	this.w[0]=x;
};

DBIG.prototype={

/* set this=0 */
	zero: function()
	{
		for (var i=0;i<ROM.DNLEN;i++) this.w[i]=0;
		return this;
	},

/* set this=b */
	copy: function(b)
	{
		for (var i=0;i<ROM.DNLEN;i++) this.w[i]=b.w[i];
		return this;
	},


/* copy from BIG */
	hcopy: function(b)
	{
		var i;
		for (i=0;i<ROM.NLEN;i++) this.w[i]=b.w[i];
		for (i=ROM.NLEN;i<ROM.DNLEN;i++) this.w[i]=0;
		return this;
	},

/* normalise this */
	norm: function()
	{
		var d,carry=0;
		for (var i=0;i<ROM.DNLEN-1;i++)
		{
			d=this.w[i]+carry;
			this.w[i]=d&ROM.MASK;
			carry=d>>ROM.BASEBITS;
		}
		this.w[ROM.DNLEN-1]=(this.w[ROM.DNLEN-1]+carry);
		return this;
	},

/* set this[i]+=x*y+c, and return high part */
	muladd: function(x,y,c,i)
	{
		var prod=x*y+c+this.w[i];
		this.w[i]=prod&ROM.MASK;
		return ((prod-this.w[i])*ROM.MODINV);
	},

/* shift this right by k bits */
	shr: function(k)
	{
		var i,n=k%ROM.BASEBITS;
		var m=Math.floor(k/ROM.BASEBITS);
		for (i=0;i<ROM.DNLEN-m-1;i++)
			this.w[i]=(this.w[m+i]>>n)|((this.w[m+i+1]<<(ROM.BASEBITS-n))&ROM.MASK);
		this.w[ROM.DNLEN-m-1]=this.w[ROM.DNLEN-1]>>n;
		for (i=ROM.DNLEN-m;i<ROM.DNLEN;i++) this.w[i]=0;
		return this;
	},

/* shift this left by k bits */
	shl: function(k)
	{
		var i,n=k%ROM.BASEBITS;
		var m=Math.floor(k/ROM.BASEBITS);

		this.w[ROM.DNLEN-1]=((this.w[ROM.DNLEN-1-m]<<n))|(this.w[ROM.DNLEN-m-2]>>(ROM.BASEBITS-n));
		for (i=ROM.DNLEN-2;i>m;i--)
			this.w[i]=((this.w[i-m]<<n)&ROM.MASK)|(this.w[i-m-1]>>(ROM.BASEBITS-n));
		this.w[m]=(this.w[0]<<n)&ROM.MASK;
		for (i=0;i<m;i++) this.w[i]=0;
		return this;
	},

/* this+=x */
	add: function(x)
	{
		for (var i=0;i<ROM.DNLEN;i++)
			this.w[i]+=x.w[i];
	},

/* this-=x */
	sub: function(x)
	{
		for (var i=0;i<ROM.DNLEN;i++)
			this.w[i]-=x.w[i];
	},

/* return number of bits in this */
	nbits: function()
	{
		var bts,k=ROM.DNLEN-1;
		var c;
		this.norm();
		while (k>=0 && this.w[k]===0) k--;
		if (k<0) return 0;
		bts=ROM.BASEBITS*k;
		c=this.w[k];
		while (c!==0) {c=Math.floor(c/2); bts++;}
		return bts;
	},

/* convert this to string */
	toString: function()
	{

		var b;
		var s="";
		var len=this.nbits();
		if (len%4===0) len=Math.floor(len/4);
		else {len=Math.floor(len/4); len++;}

		for (var i=len-1;i>=0;i--)
		{
			b=new DBIG(0);
			b.copy(this);
			b.shr(i*4);
			s+=(b.w[0]&15).toString(16);
		}
		return s;
	},

/* reduces this DBIG mod a BIG, and returns the BIG */
	mod: function(c)
	{
		var k=0;
		this.norm();
		var m=new DBIG(0);
		m.hcopy(c);
		var r=new BIG(0);
		r.hcopy(this);

		if (DBIG.comp(this,m)<0) return r;

		do
		{
			m.shl(1);
			k++;
		}
		while (DBIG.comp(this,m)>=0);

		while (k>0)
		{
			m.shr(1);
			if (DBIG.comp(this,m)>=0)
			{
				this.sub(m);
				this.norm();
			}
			k--;
		}

		r.hcopy(this);
		return r;
	},

/* this/=c */
	div: function(c)
	{
		var k=0;
		var m=new DBIG(0); m.hcopy(c);
		var a=new BIG(0);
		var e=new BIG(1);
		this.norm();

		while (DBIG.comp(this,m)>=0)
		{
			e.fshl(1);
			m.shl(1);
			k++;
		}

		while (k>0)
		{
			m.shr(1);
			e.shr(1);
			if (DBIG.comp(this,m)>0)
			{
				a.add(e);
				a.norm();
				this.sub(m);
				this.norm();
			}
			k--;
		}
		return a;
	},

/* split this DBIG at position n, return higher half, keep lower half */
	split: function(n)
	{
		var t=new BIG(0);
		var nw,m=n%ROM.BASEBITS;
		var carry=this.w[ROM.DNLEN-1]<<(ROM.BASEBITS-m);


		for (var i=ROM.DNLEN-2;i>=ROM.NLEN-1;i--)
		{
			nw=(this.w[i]>>m)|carry;
			carry=(this.w[i]<<(ROM.BASEBITS-m))&ROM.MASK;
			t.w[i-ROM.NLEN+1]=nw;
		}
		this.w[ROM.NLEN-1]&=((1<<m)-1);

		return t;
	}

};

/* Compare a and b, return 0 if a==b, -1 if a<b, +1 if a>b. Inputs must be normalised */
DBIG.comp=function(a,b)
{
	for (var i=ROM.DNLEN-1;i>=0;i--)
	{
		if (a.w[i]==b.w[i]) continue;
		if (a.w[i]>b.w[i]) return 1;
		else  return -1;
	}
	return 0;
};