lnd.xprv/shachain/utils.go

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package shachain
import (
"encoding/hex"
"github.com/roasbeef/btcd/chaincfg/chainhash"
)
// changeBit is a functio that function that flips a bit of the hash at a
// particluar bit-index. You should be aware that the bit flipping in this
// function a bit strange, example:
// hash: [0b00000000, 0b00000000, ... 0b00000000]
// 0 1 ... 31
//
// byte: 0 0 0 0 0 0 0 0
// 7 6 5 4 3 2 1 0
//
// By flipping the bit at 7 position you will flip the first bit in hash and by
// flipping the bit at 8 position you will flip the 16 bit in hash.
func changeBit(hash []byte, position uint8) []byte {
byteNumber := position / 8
bitNumber := position % 8
hash[byteNumber] ^= (1 << bitNumber)
return hash
}
// getBit return bit on index at position.
func getBit(index index, position uint8) uint8 {
return uint8((uint64(index) >> position) & 1)
}
func getPrefix(index index, position uint8) uint64 {
// + -------------------------- +
// | № | value | mask | return |
// + -- + ----- + ---- + ------ +
// | 63 | 1 | 0 | 0 |
// | 62 | 0 | 0 | 0 |
// | 61 | 1 | 0 | 0 |
// ....
// | 4 | 1 | 0 | 0 |
// | 3 | 1 | 0 | 0 |
// | 2 | 1 | 1 | 1 | <--- position
// | 1 | 0 | 1 | 0 |
// | 0 | 1 | 1 | 1 |
// + -- + ----- + ---- + ------ +
var zero uint64 = 0
mask := (zero - 1) - uint64((1<<position)-1)
return (uint64(index) & mask)
}
// countTrailingZeros count number of of trailing zero bits, this function is
// used to determine the number of element bucket.
func countTrailingZeros(index index) uint8 {
var zeros uint8 = 0
for ; zeros < maxHeight; zeros++ {
if getBit(index, zeros) != 0 {
break
}
}
return zeros
}
// hashFromString takes a hex-encoded string as input and creates an instane of
// chainhash.Hash. The chainhash.NewHashFromStr function not suitable because
// it reverse the given hash.
func hashFromString(s string) (*chainhash.Hash, error) {
// Return an error if hash string is too long.
if len(s) > chainhash.MaxHashStringSize {
return nil, chainhash.ErrHashStrSize
}
// Hex decoder expects the hash to be a multiple of two.
if len(s)%2 != 0 {
s = "0" + s
}
// Convert string hash to bytes.
buf, err := hex.DecodeString(s)
if err != nil {
return nil, err
}
hash, err := chainhash.NewHash(buf)
if err != nil {
return nil, err
}
return hash, nil
}