DBIG.go

/*
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.
*/

/* MiotCL double length DBIG number class */ 


package main

import "strconv"
//import "fmt"

func NewDBIG() *DBIG {
	b:=new(DBIG)
	for i:=0;i<DNLEN;i++ {
		b.w[i]=0
	}
	return b
}

func NewDBIGcopy(x *DBIG) *DBIG {
	b:=new(DBIG)
	for i:=0;i<DNLEN;i++ {
		b.w[i]=x.w[i]
	}
	return b
}

func NewDBIGscopy(x *BIG) *DBIG {
	b:=new(DBIG)
	for i:=0;i<NLEN-1;i++ {
		b.w[i]=x.w[i]
	}
	b.w[NLEN-1]=x.get(NLEN-1)&BMASK /* top word normalized */
	b.w[NLEN]=x.get(NLEN-1)>>BASEBITS

	for i:=NLEN+1;i<DNLEN;i++  {b.w[i]=0}
	return b
}

/* normalise this */
func (r *DBIG) norm() {
	carry:=Chunk(0)
	for i:=0;i<DNLEN-1;i++ {
		d:=r.w[i]+carry
		r.w[i]=d&BMASK
		carry=d>>BASEBITS
	}
	r.w[DNLEN-1]=(r.w[DNLEN-1]+carry)
}

/* split DBIG at position n, return higher half, keep lower half */
func (r *DBIG) split(n uint) *BIG {
	t:=NewBIG()
	m:=n%BASEBITS;
	carry:=r.w[DNLEN-1]<<(BASEBITS-m)

	for i:=DNLEN-2;i>=NLEN-1;i-- {
		nw:=(r.w[i]>>m)|carry;
		carry=(r.w[i]<<(BASEBITS-m))&BMASK;
		t.set(i-NLEN+1,nw);
	}
	r.w[NLEN-1]&=((Chunk(1)<<m)-1)
	return t;
}

func (r *DBIG) cmove(g *DBIG,d int){
	var b=Chunk(-d)

	for i:=0;i<DNLEN;i++ {
		r.w[i]^=(r.w[i]^g.w[i])&b
	}
}

/* Compare a and b, return 0 if a==b, -1 if a<b, +1 if a>b. Inputs must be normalised */
func dcomp(a *DBIG,b *DBIG) int {
	for i:=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
}

/* Copy from another BIG */
func (r *DBIG) copy(x *DBIG) {
	for i:=0;i<DNLEN;i++ {
		r.w[i]=x.w[i]
	}
}

func (r *DBIG) add(x *DBIG) {
	for i:=0;i<DNLEN;i++ {
		r.w[i]=r.w[i]+x.w[i] 
	}
}

/* this-=x */
func (r *DBIG) sub(x *DBIG) {
	for i:=0;i<DNLEN;i++ {
		r.w[i]=r.w[i]-x.w[i] 
	}
} 

/* general shift left */
func (r *DBIG) shl(k uint) {
	n:=k%BASEBITS
	m:=int(k/BASEBITS)

	r.w[DNLEN-1]=((r.w[DNLEN-1-m]<<n))|(r.w[DNLEN-m-2]>>(BASEBITS-n))
	for i:=DNLEN-2;i>m;i-- {
		r.w[i]=((r.w[i-m]<<n)&BMASK)|(r.w[i-m-1]>>(BASEBITS-n))
	}
	r.w[m]=(r.w[0]<<n)&BMASK; 
	for i:=0;i<m;i++ {r.w[i]=0}
}

/* general shift right */
func (r *DBIG) shr(k uint) {
	n:=(k%BASEBITS)
	m:=int(k/BASEBITS)	
	for i:=0;i<DNLEN-m-1;i++ {
		r.w[i]=(r.w[m+i]>>n)|((r.w[m+i+1]<<(BASEBITS-n))&BMASK)
	}
	r.w[DNLEN-m-1]=r.w[DNLEN-1]>>n;
	for i:=DNLEN-m;i<DNLEN;i++ {r.w[i]=0}
}

/* reduces this DBIG mod a BIG, and returns the BIG */
func (r *DBIG) mod(c *BIG) *BIG {
	r.norm()
	m:=NewDBIGscopy(c)
	dr:=NewDBIG();

	if dcomp(r,m)<0 {
		return NewBIGdcopy(r)
	}

	m.shl(1);
	k:=1;
		
	for dcomp(r,m)>=0 {
		m.shl(1);
		k++;
	}

	for k>0 {
		m.shr(1);

		dr.copy(r);
		dr.sub(m);
		dr.norm();
		r.cmove(dr,int(1-((dr.w[DNLEN-1]>>uint(CHUNK-1))&1)));
/*
		if dcomp(r,m)>=0 {
			r.sub(m);
			r.norm();
		} */
		k--;
	}
	return NewBIGdcopy(r)
}

/* return this/c */
func (r *DBIG) div(c *BIG) *BIG {
	var d int
	k:=0
	m:=NewDBIGscopy(c)
	a:=NewBIGint(0)
	e:=NewBIGint(1)
	sr:=NewBIG()
	dr:=NewDBIG()
	r.norm()

	for dcomp(r,m)>=0 {
		e.fshl(1)
		m.shl(1)
		k++
	}

	for k>0 {
		m.shr(1)
		e.shr(1)

		dr.copy(r);
		dr.sub(m);
		dr.norm();
		d=int(1-((dr.w[DNLEN-1]>>uint(CHUNK-1))&1));
		r.cmove(dr,d);
		sr.copy(a);
		sr.add(e);
		sr.norm();
		a.cmove(sr,d);

/*
		if dcomp(r,m)>0 {
			a.add(e)
			a.norm()
			r.sub(m)
			r.norm()
		} */
		k--
	}
	return a
}

/* Convert to Hex String */
func (r *DBIG) toString() string {
	s:=""
	len:=r.nbits()

	if len%4==0 {
		len/=4
	} else {
		len/=4 
		len++

	}

	for i:=len-1;i>=0;i-- {
		b:=NewDBIGcopy(r)
		
		b.shr(uint(i*4))
		s+=strconv.FormatInt(int64(b.w[0]&15),16)
	}
	return s
}

/* return number of bits */
func (r *DBIG) nbits() int {
	k:=DNLEN-1
	r.norm()
	for (k>=0 && r.w[k]==0) {k--}
	if k<0 {return 0}
	bts:=int(BASEBITS)*k;
	c:=r.w[k];
	for c!=0 {c/=2; bts++}
	return bts
}