trie: implements vlc coder

trie/internal/vlc/buffer.go

@@ -0,0 +1,59 @@
+// Copyright (c) 2023 The VeChainThor developers
+
+// Distributed under the GNU Lesser General Public License v3.0 software license, see the accompanying
+// file LICENSE or <https://www.gnu.org/licenses/lgpl-3.0.html>
+
+// Package vlc implements variable length coding.
+//
+// It's much simpler and a bit faster than RLP.
+// Trie nodes stored in database are encoded using VLC.
+package vlc
+
+import "encoding/binary"
+
+// Buffer is essentially a byte slice. It holds encoded elements.
+type Buffer []byte
+
+// Truncate truncates the buffer to size.
+func (b *Buffer) Truncate(size int) {
+	*b = (*b)[:size]
+}
+
+// PutUint puts the uint value.
+func (b *Buffer) PutUint(i uint64) {
+	*b = binary.AppendUvarint(*b, i)
+}
+
+// PutString puts the string value.
+func (b *Buffer) PutString(str []byte) {
+	*b = binary.AppendUvarint(*b, uint64(len(str)))
+	*b = append(*b, str...)
+}
+
+// PutFunc puts the string value returned by func build.
+// The build func should not modify existing content of buf,
+// and should follow the behavior like append.
+func (b *Buffer) PutFunc(build func(buf []byte) []byte) {
+	offset := len(*b)
+	*b = append(*b, make([]byte, binary.MaxVarintLen64)...)
+	*b = build(*b)
+
+	str := (*b)[offset+binary.MaxVarintLen64:]
+	b.Truncate(offset)
+	b.PutString(str)
+}
+
+// SplitString extracts a string and returns rest bytes.
+// It'll panic if errored.
+func SplitString(buf []byte) (str []byte, rest []byte) {
+	size, n := binary.Uvarint(buf)
+	buf = buf[n:]
+	return buf[:size], buf[size:]
+}
+
+// SplitUint extracts uint64 and returns rest bytes.
+// It'll panic if errored.
+func SplitUint(buf []byte) (uint64, []byte) {
+	v, n := binary.Uvarint(buf)
+	return v, buf[n:]
+}