go/src/github.com/miracl/amcl-go/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.
*/

/* AMCL double length DBIG number class */

package amcl

import "strconv"

type DBIG struct {
	w [2 * NLEN]int64
}

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) & MASK /* top word normalized */
	b.w[NLEN] = x.get(NLEN-1) >> BASEBITS

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

/* set this[i]+=x*y+c, and return high part */

func (r *DBIG) muladd(a int64, b int64, c int64, i int) int64 {
	x0 := a & HMASK
	x1 := (a >> HBITS)
	y0 := b & HMASK
	y1 := (b >> HBITS)
	bot := x0 * y0
	top := x1 * y1
	mid := x0*y1 + x1*y0
	x0 = mid & HMASK
	x1 = (mid >> HBITS)
	bot += x0 << HBITS
	bot += c
	bot += r.w[i]
	top += x1
	carry := bot >> BASEBITS
	bot &= MASK
	top += carry
	r.w[i] = bot
	return top
}

/* normalise this */
func (r *DBIG) norm() {
	var carry int64 = 0
	for i := 0; i < DNLEN-1; i++ {
		d := r.w[i] + carry
		r.w[i] = d & MASK
		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)) & MASK
		t.set(i-NLEN+1, nw)
	}
	r.w[NLEN-1] &= ((int64(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 */
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
}

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) & MASK) | (r.w[i-m-1] >> (BASEBITS - n))
	}
	r.w[m] = (r.w[0] << n) & MASK
	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)) & MASK)
	}
	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)

	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)
		if dcomp(r, m) >= 0 {
			r.sub(m)
			r.norm()
		}
		k--
	}
	return NewBIGdcopy(r)
}

/* return this/c */
func (r *DBIG) div(c *BIG) *BIG {
	k := 0
	m := NewDBIGscopy(c)
	a := NewBIGint(0)
	e := NewBIGint(1)
	r.norm()

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

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