Initial project import

tools/v/vlib/compress/lz/lzw.v

@@ -0,0 +1,92 @@
+module lz
+
+// compress_lzw compresses data using a pure-V LZW dictionary stream.
+pub fn compress_lzw(data []u8) ![]u8 {
+	mut payload := []u8{}
+	mut dict := map[string]int{}
+	for i in 0 .. 256 {
+		dict[[u8(i)].bytestr()] = i
+	}
+	mut next_code := 256
+	mut word := ''
+
+	for b in data {
+		symbol := [b].bytestr()
+		candidate := word + symbol
+		if candidate in dict {
+			word = candidate
+			continue
+		}
+		if word != '' {
+			encode_uvarint(mut payload, u64(dict[word]))
+		}
+		dict[candidate] = next_code
+		next_code++
+		word = symbol
+	}
+
+	if word != '' {
+		encode_uvarint(mut payload, u64(dict[word]))
+	}
+
+	return wrap_payload(.lzw, data, payload)
+}
+
+// decompress_lzw decompresses data produced by compress_lzw.
+pub fn decompress_lzw(data []u8) ![]u8 {
+	payload, expected_len := unwrap_payload(data, .lzw)!
+	if payload.len == 0 {
+		if expected_len == i64(0) {
+			return []u8{}
+		}
+		return error('invalid lzw stream: missing codes')
+	}
+
+	mut dict := map[int][]u8{}
+	for i in 0 .. 256 {
+		dict[i] = [u8(i)]
+	}
+	mut next_code := 256
+	mut pos := 0
+
+	first_code, next_pos, ok := decode_uvarint(payload, pos)
+	if !ok {
+		return error('invalid lzw stream: bad initial code')
+	}
+	pos = next_pos
+	if int(first_code) !in dict {
+		return error('invalid lzw stream: unknown initial code')
+	}
+	mut word := dict[int(first_code)].clone()
+	mut out := word.clone()
+
+	for pos < payload.len {
+		code_u64, new_pos, ok_code := decode_uvarint(payload, pos)
+		if !ok_code {
+			return error('invalid lzw stream: bad code')
+		}
+		pos = new_pos
+		code := int(code_u64)
+		mut entry := []u8{}
+		if code in dict {
+			entry = dict[code].clone()
+		} else if code == next_code {
+			entry = word.clone()
+			entry << word[0]
+		} else {
+			return error('invalid lzw stream: unknown code')
+		}
+
+		out << entry
+		mut new_entry := word.clone()
+		new_entry << entry[0]
+		dict[next_code] = new_entry
+		next_code++
+		word = entry.clone()
+	}
+
+	if i64(out.len) != expected_len {
+		return error('invalid lzw stream: length mismatch')
+	}
+	return out
+}