156 lines
3 KiB
Go
156 lines
3 KiB
Go
package bigint
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import (
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"encoding/binary"
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"math/big"
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"math/bits"
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)
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const (
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// MaxBytesLen is the maximum length of serialized integer suitable for Neo VM.
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MaxBytesLen = 33 // 32 bytes for 256-bit integer plus 1 if padding needed
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// wordSizeBytes is a size of a big.Word (uint) in bytes.
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wordSizeBytes = bits.UintSize / 8
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)
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// FromBytes converts data in little-endian format to
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// an integer.
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func FromBytes(data []byte) *big.Int {
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n := new(big.Int)
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size := len(data)
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if size == 0 {
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if data == nil {
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panic("nil slice provided to `FromBytes`")
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}
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return big.NewInt(0)
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}
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isNeg := data[size-1]&0x80 != 0
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size = getEffectiveSize(data, isNeg)
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if size == 0 {
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if isNeg {
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return big.NewInt(-1)
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}
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return big.NewInt(0)
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}
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lw := size / wordSizeBytes
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ws := make([]big.Word, lw+1)
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for i := 0; i < lw; i++ {
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base := i * wordSizeBytes
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for j := base + 7; j >= base; j-- {
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ws[i] <<= 8
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ws[i] ^= big.Word(data[j])
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}
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}
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for i := size - 1; i >= lw*wordSizeBytes; i-- {
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ws[lw] <<= 8
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ws[lw] ^= big.Word(data[i])
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}
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if isNeg {
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for i := 0; i <= lw; i++ {
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ws[i] = ^ws[i]
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}
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shift := byte(wordSizeBytes-size%wordSizeBytes) * 8
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ws[lw] = ws[lw] & (^big.Word(0) >> shift)
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n.SetBits(ws)
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n.Neg(n)
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return n.Sub(n, big.NewInt(1))
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}
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return n.SetBits(ws)
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}
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// getEffectiveSize returns minimal number of bytes required
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// to represent a number (two's complement for negatives).
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func getEffectiveSize(buf []byte, isNeg bool) int {
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var b byte
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if isNeg {
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b = 0xFF
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}
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size := len(buf)
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for ; size > 0; size-- {
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if buf[size-1] != b {
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break
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}
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}
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return size
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}
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// ToBytes converts integer to a slice in little-endian format.
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// Note: NEO3 serialization differs from default C# BigInteger.ToByteArray()
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// when n == 0. For zero is equal to empty slice in NEO3.
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// https://github.com/neo-project/neo-vm/blob/master/src/neo-vm/Types/Integer.cs#L16
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func ToBytes(n *big.Int) []byte {
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return ToPreallocatedBytes(n, []byte{})
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}
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// ToPreallocatedBytes converts integer to a slice in little-endian format using given
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// byte array for conversion result.
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func ToPreallocatedBytes(n *big.Int, data []byte) []byte {
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sign := n.Sign()
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if sign == 0 {
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return data
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}
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var ws []big.Word
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if sign == 1 {
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ws = n.Bits()
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} else {
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n1 := new(big.Int).Add(n, big.NewInt(1))
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if n1.Sign() == 0 { // n == -1
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return append(data, 0xFF)
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}
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ws = n1.Bits()
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}
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lb := len(ws) * wordSizeBytes
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if c := cap(data); c < lb {
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data = make([]byte, lb, lb+1)
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} else {
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data = data[:lb]
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}
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data = wordsToBytes(ws, data)
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size := len(data)
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for ; data[size-1] == 0; size-- {
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}
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data = data[:size]
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if data[size-1]&0x80 != 0 {
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data = append(data, 0)
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}
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if sign == -1 {
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for i := range data {
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data[i] = ^data[i]
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}
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}
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return data
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}
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func wordsToBytes(ws []big.Word, bs []byte) []byte {
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if wordSizeBytes == 8 {
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for i := range ws {
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binary.LittleEndian.PutUint64(bs[i*wordSizeBytes:], uint64(ws[i]))
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}
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} else {
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for i := range ws {
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binary.LittleEndian.PutUint32(bs[i*wordSizeBytes:], uint32(ws[i]))
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}
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}
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return bs
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}
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