neoneo-go/pkg/encoding/bigint/bigint.go

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package bigint
import (
"math/big"
"math/bits"
"github.com/nspcc-dev/neo-go/pkg/util/slice"
)
const (
// MaxBytesLen is the maximum length of a serialized integer suitable for Neo VM.
MaxBytesLen = 32 // 256-bit signed integer
// wordSizeBytes is a size of a big.Word (uint) in bytes.
wordSizeBytes = bits.UintSize / 8
)
var bigOne = big.NewInt(1)
// FromBytesUnsigned converts data in little-endian format to an unsigned integer.
func FromBytesUnsigned(data []byte) *big.Int {
bs := slice.CopyReverse(data)
return new(big.Int).SetBytes(bs)
}
// FromBytes converts data in little-endian format to
// an integer.
func FromBytes(data []byte) *big.Int {
n := new(big.Int)
size := len(data)
if size == 0 {
if data == nil {
panic("nil slice provided to `FromBytes`")
}
return big.NewInt(0)
}
isNeg := data[size-1]&0x80 != 0
size = getEffectiveSize(data, isNeg)
if size == 0 {
if isNeg {
return big.NewInt(-1)
}
return big.NewInt(0)
}
lw := size / wordSizeBytes
ws := make([]big.Word, lw+1)
for i := 0; i < lw; i++ {
base := i * wordSizeBytes
for j := base + 7; j >= base; j-- {
ws[i] <<= 8
ws[i] ^= big.Word(data[j])
}
}
for i := size - 1; i >= lw*wordSizeBytes; i-- {
ws[lw] <<= 8
ws[lw] ^= big.Word(data[i])
}
if isNeg {
for i := 0; i <= lw; i++ {
ws[i] = ^ws[i]
}
shift := byte(wordSizeBytes-size%wordSizeBytes) * 8
ws[lw] = ws[lw] & (^big.Word(0) >> shift)
n.SetBits(ws)
n.Neg(n)
return n.Sub(n, bigOne)
}
return n.SetBits(ws)
}
// getEffectiveSize returns the minimal number of bytes required
// to represent a number (two's complement for negatives).
func getEffectiveSize(buf []byte, isNeg bool) int {
var b byte
if isNeg {
b = 0xFF
}
size := len(buf)
for ; size > 0; size-- {
if buf[size-1] != b {
break
}
}
return size
}
// ToBytes converts an integer to a slice in little-endian format.
// Note: NEO3 serialization differs from default C# BigInteger.ToByteArray()
// when n == 0. For zero is equal to empty slice in NEO3.
// https://github.com/neo-project/neo-vm/blob/master/src/neo-vm/Types/Integer.cs#L16
func ToBytes(n *big.Int) []byte {
return ToPreallocatedBytes(n, []byte{})
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}
// ToPreallocatedBytes converts an integer to a slice in little-endian format using the given
// byte array for conversion result.
func ToPreallocatedBytes(n *big.Int, data []byte) []byte {
sign := n.Sign()
if sign == 0 {
return data[:0]
}
if sign < 0 {
n.Add(n, bigOne)
defer func() { n.Sub(n, bigOne) }()
if n.Sign() == 0 { // n == -1
return append(data[:0], 0xFF)
}
}
lb := n.BitLen()/8 + 1
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if c := cap(data); c < lb {
data = make([]byte, lb)
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} else {
data = data[:lb]
}
_ = n.FillBytes(data)
slice.Reverse(data)
if sign == -1 {
for i := range data {
data[i] = ^data[i]
}
}
return data
}