bigint.go

/*
 * Copyright (C) 2018 The ontology Authors
 * This file is part of The ontology library.
 *
 * The ontology is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * The ontology is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with The ontology.  If not, see <http://www.gnu.org/licenses/>.
 */

 package ont

 import "math/big"
 
 func bytesReverse(u []byte) []byte {
	 for i, j := 0, len(u)-1; i < j; i, j = i+1, j-1 {
		 u[i], u[j] = u[j], u[i]
	 }
	 return u
 }
 
 var bigOne = big.NewInt(1)
 
 // neo encoding: https://docs.microsoft.com/en-us/dotnet/api/system.numerics.biginteger.tobytearray?view=netframework-4.7.2
 func BigIntToNeoBytes(data *big.Int) []byte {
	 bs := data.Bytes()
	 if len(bs) == 0 {
		 return []byte{}
	 }
	 // golang big.Int use big-endian
	 bytesReverse(bs)
	 // bs now is little-endian
	 if data.Sign() < 0 {
		 for i, b := range bs {
			 bs[i] = ^b
		 }
		 for i := 0; i < len(bs); i++ {
			 if bs[i] == 255 {
				 bs[i] = 0
			 } else {
				 bs[i] += 1
				 break
			 }
		 }
		 if bs[len(bs)-1] < 128 {
			 bs = append(bs, 255)
		 }
	 } else {
		 if bs[len(bs)-1] >= 128 {
			 bs = append(bs, 0)
		 }
	 }
	 return bs
 }
 
 func BigIntFromNeoBytes(ba []byte) *big.Int {
	 res := big.NewInt(0)
	 l := len(ba)
	 if l == 0 {
		 return res
	 }
 
	 bytes := make([]byte, 0, l)
	 bytes = append(bytes, ba...)
	 bytesReverse(bytes)
 
	 if bytes[0]>>7 == 1 {
		 for i, b := range bytes {
			 bytes[i] = ^b
		 }
 
		 temp := big.NewInt(0)
		 temp.SetBytes(bytes)
		 temp.Add(temp, bigOne)
		 bytes = temp.Bytes()
		 res.SetBytes(bytes)
		 return res.Neg(res)
	 }
 
	 res.SetBytes(bytes)
	 return res
 }