Decompress LZ4 data

lz4_decompress.rb

def lz4_decompress(path)
    def read_value(data, pos, size)
        case size
        when 1; type = 'C'
        when 2; type = 'S'
        when 4; type = 'L'
        end
        [pos + size, data[pos, size].unpack(type)[0]]
    end

    def read_literal(data, pos, size)
        [pos + size, data[pos, size]]
    end

    data = File.open(path, "rb:ascii-8bit").read
    out = ''

    pos, content_size = read_value(data, 0, 4)
    while true
        pos, token = read_value(data, pos, 1)

        literal_length = token >> 4
        match_length = token & 0xf

        if literal_length == 15
            s = 255
            while s == 255
                pos, s = read_value(data, pos, 1)
                literal_length += s
            end
        end

        if literal_length > 0
            pos, literal = read_literal(data, pos, literal_length)
            out += literal
        end

        break if pos == data.size

        pos, offset = read_value(data, pos, 2)

        if match_length == 15
            s = 255
            while s == 255
                pos, s = read_value(data, pos, 1)
                match_length += s
            end
        end
        match_length += 4

        if match_length > offset
            repeat_literal = out[offset * -1, offset]
            match_literal = repeat_literal

            while match_literal.size < match_length
                match_literal += repeat_literal[0, match_length - match_literal.size]
            end
        else
            match_literal = out[offset * -1, match_length]
        end

        out += match_literal
    end
    out
end