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package conv
import (
"fmt"
"math/big"
"strings"
)
// BytesLe2Hex returns an hexadecimal string of a number stored in a
// little-endian order slice x.
func BytesLe2Hex(x []byte) string {
b := &strings.Builder{}
b.Grow(2*len(x) + 2)
fmt.Fprint(b, "0x")
if len(x) == 0 {
fmt.Fprint(b, "00")
}
for i := len(x) - 1; i >= 0; i-- {
fmt.Fprintf(b, "%02x", x[i])
}
return b.String()
}
// BytesLe2BigInt converts a little-endian slice x into a big-endian
// math/big.Int.
func BytesLe2BigInt(x []byte) *big.Int {
n := len(x)
b := new(big.Int)
if len(x) > 0 {
y := make([]byte, n)
for i := 0; i < n; i++ {
y[n-1-i] = x[i]
}
b.SetBytes(y)
}
return b
}
// BigInt2BytesLe stores a positive big.Int number x into a little-endian slice z.
// The slice is modified if the bitlength of x <= 8*len(z) (padding with zeros).
// If x does not fit in the slice or is negative, z is not modified.
func BigInt2BytesLe(z []byte, x *big.Int) {
xLen := (x.BitLen() + 7) >> 3
zLen := len(z)
if zLen >= xLen && x.Sign() >= 0 {
y := x.Bytes()
for i := 0; i < xLen; i++ {
z[i] = y[xLen-1-i]
}
for i := xLen; i < zLen; i++ {
z[i] = 0
}
}
}
// Uint64Le2BigInt converts a little-endian slice x into a big number.
func Uint64Le2BigInt(x []uint64) *big.Int {
n := len(x)
b := new(big.Int)
var bi big.Int
for i := n - 1; i >= 0; i-- {
bi.SetUint64(x[i])
b.Lsh(b, 64)
b.Add(b, &bi)
}
return b
}
// BigInt2Uint64Le stores a positive big.Int number x into a little-endian slice z.
// The slice is modified if the bitlength of x <= 8*len(z) (padding with zeros).
// If x does not fit in the slice or is negative, z is not modified.
func BigInt2Uint64Le(z []uint64, x *big.Int) {
xLen := (x.BitLen() + 63) >> 6 // number of 64-bit words
zLen := len(z)
if zLen >= xLen && x.Sign() > 0 {
var y, yi big.Int
y.Set(x)
two64 := big.NewInt(1)
two64.Lsh(two64, 64).Sub(two64, big.NewInt(1))
for i := 0; i < xLen; i++ {
yi.And(&y, two64)
z[i] = yi.Uint64()
y.Rsh(&y, 64)
}
}
for i := xLen; i < zLen; i++ {
z[i] = 0
}
}
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