Initial project import

tools/v/vlib/compress/lz/lz78.v

@@ -0,0 +1,85 @@
+module lz
+
+// compress_lz78 compresses data using a pure-V LZ78 dictionary stream.
+pub fn compress_lz78(data []u8) ![]u8 {
+	mut payload := []u8{}
+	mut dict := map[string]int{}
+	mut next_index := 1
+	mut word := []u8{}
+
+	for b in data {
+		mut candidate := word.clone()
+		candidate << b
+		candidate_key := candidate.bytestr()
+		if candidate_key in dict {
+			word = candidate.clone()
+			continue
+		}
+
+		prefix_index := if word.len == 0 { 0 } else { dict[word.bytestr()] }
+		encode_uvarint(mut payload, u64(prefix_index))
+		payload << u8(1)
+		payload << b
+		dict[candidate_key] = next_index
+		next_index++
+		word.clear()
+	}
+
+	if word.len > 0 {
+		final_index := dict[word.bytestr()]
+		encode_uvarint(mut payload, u64(final_index))
+		payload << u8(0)
+	}
+
+	return wrap_payload(.lz78, data, payload)
+}
+
+// decompress_lz78 decompresses data produced by compress_lz78.
+pub fn decompress_lz78(data []u8) ![]u8 {
+	payload, expected_len := unwrap_payload(data, .lz78)!
+	mut out := []u8{cap: int(expected_len)}
+	mut dict := map[int][]u8{}
+	mut next_index := 1
+	mut pos := 0
+
+	for pos < payload.len {
+		prefix, next_pos, ok := decode_uvarint(payload, pos)
+		if !ok {
+			return error('invalid lz78 stream: bad prefix index')
+		}
+		pos = next_pos
+		if pos >= payload.len {
+			return error('invalid lz78 stream: missing suffix flag')
+		}
+		has_suffix := payload[pos]
+		pos++
+
+		mut phrase := if prefix == 0 {
+			[]u8{}
+		} else {
+			if int(prefix) !in dict {
+				return error('invalid lz78 stream: unknown prefix index')
+			}
+			dict[int(prefix)].clone()
+		}
+
+		if has_suffix == 1 {
+			if pos >= payload.len {
+				return error('invalid lz78 stream: missing suffix byte')
+			}
+			phrase << payload[pos]
+			pos++
+		} else if has_suffix != 0 {
+			return error('invalid lz78 stream: bad suffix flag')
+		}
+
+		out << phrase
+		dict[next_index] = phrase
+		next_index++
+	}
+
+	if i64(out.len) != expected_len {
+		return error('invalid lz78 stream: length mismatch')
+	}
+	return out
+}