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| // Copyright (C) 2019-2023 Algorand, Inc. | ||
| // This file is part of go-algorand | ||
| // | ||
| // go-algorand is free software: you can redistribute it and/or modify | ||
| // it under the terms of the GNU Affero General Public License as | ||
| // published by the Free Software Foundation, either version 3 of the | ||
| // License, or (at your option) any later version. | ||
| // | ||
| // go-algorand is distributed in the hope that it will be useful, | ||
| // but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| // GNU Affero General Public License for more details. | ||
| // | ||
| // You should have received a copy of the GNU Affero General Public License | ||
| // along with go-algorand. If not, see <https://www.gnu.org/licenses/>. | ||
|
|
||
| package nibbles | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "errors" | ||
| ) | ||
|
|
||
| // Nibbles are 4-bit values stored in an 8-bit byte arrays | ||
| type Nibbles []byte | ||
|
|
||
| const ( | ||
| // oddIndicator for serialization when the last nibble in a byte array | ||
| // is not part of the nibble array. | ||
| oddIndicator = 0x01 | ||
| // evenIndicator for when it is. | ||
| evenIndicator = 0x03 | ||
| ) | ||
|
|
||
| // Pack the nibble array into a byte array. | ||
| // Return the byte array and a bool indicating if the last byte is a full byte or | ||
| // only the high 4 bits are part of the encoding | ||
| // the last four bits of a oddLength byte encoding will always be zero. | ||
| // Allocates a new byte slice. | ||
| // | ||
| // [0x1, 0x2, 0x3] -> [0x12, 0x30], true | ||
| // [0x1, 0x2, 0x3, 0x4] -> [0x12, 0x34], false | ||
| // [0x1] -> [0x10], true | ||
| // [] -> [], false | ||
| func Pack(nyb Nibbles) ([]byte, bool) { | ||
| length := len(nyb) | ||
| data := make([]byte, length/2+length%2, length/2+length%2+1) | ||
| for i := 0; i < length; i++ { | ||
| if i%2 == 0 { | ||
| data[i/2] = nyb[i] << 4 | ||
| } else { | ||
| data[i/2] = data[i/2] | nyb[i] | ||
| } | ||
| } | ||
|
|
||
| return data, length%2 != 0 | ||
| } | ||
|
|
||
| // Equal returns true if the two nibble arrays are equal | ||
| // [0x1, 0x2, 0x3], [0x1, 0x2, 0x3] -> true | ||
| // [0x1, 0x2, 0x3], [0x1, 0x2, 0x4] -> false | ||
| // [0x1, 0x2, 0x3], [0x1] -> false | ||
| // [0x1, 0x2, 0x3], [0x1, 0x2, 0x3, 0x4] -> false | ||
| // [], [] -> true | ||
| // [], [0x1] -> false | ||
| func Equal(nyb1 Nibbles, nyb2 Nibbles) bool { | ||
| return bytes.Equal(nyb1, nyb2) | ||
| } | ||
|
|
||
| // ShiftLeft returns a slice of nyb1 that contains the Nibbles after the first | ||
| // numNibbles | ||
| func ShiftLeft(nyb1 Nibbles, numNibbles int) Nibbles { | ||
| if numNibbles <= 0 { | ||
| return nyb1 | ||
| } | ||
| if numNibbles > len(nyb1) { | ||
| return nyb1[:0] | ||
| } | ||
|
|
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| return nyb1[numNibbles:] | ||
| } | ||
|
|
||
| // SharedPrefix returns a slice from nyb1 that contains the shared prefix | ||
| // between nyb1 and nyb2 | ||
| func SharedPrefix(nyb1 Nibbles, nyb2 Nibbles) Nibbles { | ||
| minLength := len(nyb1) | ||
| if len(nyb2) < minLength { | ||
| minLength = len(nyb2) | ||
| } | ||
| for i := 0; i < minLength; i++ { | ||
| if nyb1[i] != nyb2[i] { | ||
| return nyb1[:i] | ||
| } | ||
| } | ||
| return nyb1[:minLength] | ||
| } | ||
|
|
||
| // Serialize returns a byte array that represents the Nibbles | ||
| // an empty nibble array is serialized as a single byte with value 0x3 | ||
| // as the empty nibble is considered to be full width | ||
| // | ||
| // [0x1, 0x2, 0x3] -> [0x12, 0x30, 0x01] | ||
| // [0x1, 0x2, 0x3, 0x4] -> [0x12, 0x34, 0x03] | ||
| // [] -> [0x03] | ||
| func Serialize(nyb Nibbles) (data []byte) { | ||
| p, h := Pack(nyb) | ||
| if h { | ||
| // 0x01 is the odd length indicator | ||
| return append(p, oddIndicator) | ||
| } | ||
| // 0x03 is the even length indicator | ||
| return append(p, evenIndicator) | ||
| } | ||
|
|
||
| // Deserialize returns a nibble array from the byte array. | ||
| func Deserialize(encoding []byte) (Nibbles, error) { | ||
| var ns Nibbles | ||
| length := len(encoding) | ||
| if length == 0 { | ||
| return nil, errors.New("invalid encoding") | ||
| } | ||
| if encoding[length-1] == oddIndicator { | ||
| if length == 1 { | ||
| return nil, errors.New("invalid encoding") | ||
| } | ||
| ns = makeNibbles(encoding[:length-1], true) | ||
| } else if encoding[length-1] == evenIndicator { | ||
| ns = makeNibbles(encoding[:length-1], false) | ||
| } else { | ||
| return nil, errors.New("invalid encoding") | ||
| } | ||
| return ns, nil | ||
| } | ||
|
|
||
| // makeNibbles returns a nibble array from the byte array. If oddLength is true, | ||
| // the last 4 bits of the last byte of the array are ignored. | ||
| // | ||
| // [0x12, 0x30], true -> [0x1, 0x2, 0x3] | ||
| // [0x12, 0x34], false -> [0x1, 0x2, 0x3, 0x4] | ||
| // [0x12, 0x34], true -> [0x1, 0x2, 0x3] <-- last byte last 4 bits ignored | ||
| // [], false -> [] | ||
| // never to be called with [], true | ||
| // Allocates a new byte slice. | ||
| func makeNibbles(data []byte, oddLength bool) Nibbles { | ||
| length := len(data) * 2 | ||
| if oddLength { | ||
| length = length - 1 | ||
| } | ||
| ns := make([]byte, length) | ||
|
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| j := 0 | ||
| for i := 0; i < length; i++ { | ||
| if i%2 == 0 { | ||
| ns[i] = data[j] >> 4 | ||
| } else { | ||
| ns[i] = data[j] & 0x0f | ||
| j++ | ||
| } | ||
| } | ||
| return ns | ||
| } |
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