137 lines
2.3 KiB
Go
137 lines
2.3 KiB
Go
package emit
|
|
|
|
import (
|
|
"encoding/binary"
|
|
"math/big"
|
|
"math/bits"
|
|
)
|
|
|
|
// wordSizeBytes is a size of a big.Word (uint) in bytes.`
|
|
const wordSizeBytes = bits.UintSize / 8
|
|
|
|
// BytesToInt converts data in little-endian format to
|
|
// an integer.
|
|
func BytesToInt(data []byte) *big.Int {
|
|
n := new(big.Int)
|
|
size := len(data)
|
|
if size == 0 {
|
|
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, big.NewInt(1))
|
|
}
|
|
|
|
return n.SetBits(ws)
|
|
}
|
|
|
|
// getEffectiveSize returns 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
|
|
}
|
|
|
|
// IntToBytes converts integer to a slice in little-endian format.
|
|
func IntToBytes(n *big.Int) []byte {
|
|
sign := n.Sign()
|
|
if sign == 0 {
|
|
return []byte{0}
|
|
}
|
|
|
|
var ws []big.Word
|
|
if sign == 1 {
|
|
ws = n.Bits()
|
|
} else {
|
|
n1 := new(big.Int).Add(n, big.NewInt(1))
|
|
if n1.Sign() == 0 { // n == -1
|
|
return []byte{0xFF}
|
|
}
|
|
|
|
ws = n1.Bits()
|
|
}
|
|
|
|
data := wordsToBytes(ws)
|
|
|
|
size := len(data)
|
|
for ; data[size-1] == 0; size-- {
|
|
}
|
|
|
|
data = data[:size]
|
|
|
|
if data[size-1]&0x80 != 0 {
|
|
data = append(data, 0)
|
|
}
|
|
|
|
if sign == -1 {
|
|
for i := range data {
|
|
data[i] = ^data[i]
|
|
}
|
|
}
|
|
|
|
return data
|
|
}
|
|
|
|
func wordsToBytes(ws []big.Word) []byte {
|
|
lb := len(ws) * wordSizeBytes
|
|
bs := make([]byte, lb, lb+1)
|
|
|
|
if wordSizeBytes == 8 {
|
|
for i := range ws {
|
|
binary.LittleEndian.PutUint64(bs[i*wordSizeBytes:], uint64(ws[i]))
|
|
}
|
|
} else {
|
|
for i := range ws {
|
|
binary.LittleEndian.PutUint32(bs[i*wordSizeBytes:], uint32(ws[i]))
|
|
}
|
|
}
|
|
|
|
return bs
|
|
}
|