Merge remote-tracking branch 'laconic/add-path-encoders' into laconic-merge

restricted/trie/encoding.go

@@ -0,0 +1,34 @@
+package trie
+
+// HexToCompact converts a hex path to the compact encoded format
+func HexToCompact(hex []byte) []byte {
+	return hexToCompact(hex)
+}
+
+func hexToCompact(hex []byte) []byte {
+	terminator := byte(0)
+	if hasTerm(hex) {
+		terminator = 1
+		hex = hex[:len(hex)-1]
+	}
+	buf := make([]byte, len(hex)/2+1)
+	buf[0] = terminator << 5 // the flag byte
+	if len(hex)&1 == 1 {
+		buf[0] |= 1 << 4 // odd flag
+		buf[0] |= hex[0] // first nibble is contained in the first byte
+		hex = hex[1:]
+	}
+	decodeNibbles(hex, buf[1:])
+	return buf
+}
+
+func decodeNibbles(nibbles []byte, bytes []byte) {
+	for bi, ni := 0, 0; ni < len(nibbles); bi, ni = bi+1, ni+2 {
+		bytes[bi] = nibbles[ni]<<4 | nibbles[ni+1]
+	}
+}
+
+// hasTerm returns whether a hex key has the terminator flag.
+func hasTerm(s []byte) bool {
+	return len(s) > 0 && s[len(s)-1] == 16
+}