do not save size if not needed

Author: jermp

include/interpolative_coding.hpp

@@ -202,11 +202,11 @@ struct centered_minimal {
 
 template <typename Writer>
 struct encoder {
-    void encode(uint32_t const* input, uint32_t n) {
+    void encode(uint32_t const* input, uint32_t n, bool write_size = true) {
         if (!n) return;
         uint32_t universe = input[n - 1];
         write_binary(universe);
-        write_binary(n);
+        if (write_size) write_binary(n);
         encode(input, n - 1, 0, universe);
     }
 
@@ -261,6 +261,13 @@ struct decoder {
         return n;
     }
 
+    uint32_t decode(uint32_t* out, uint32_t n) {
+        uint32_t universe = read_binary();
+        out[n - 1] = universe;
+        decode(out, n - 1, 0, universe);
+        return n;
+    }
+
     uint32_t decode(uint32_t const* encoded, uint32_t* out) {
         m_reader.init(encoded);
         return decode(out);

test/example.cpp

@@ -11,26 +11,49 @@ void test(std::vector<uint32_t> const& in) {
     }
     std::cout << std::endl;
 
-    uint32_t n = in.size();
+    {
+        uint32_t n = in.size();
+        encoder<typename BinaryCode::writer> enc;
+        enc.encode(in.data(), n);  // save n by feault
+        std::vector<uint32_t> out(n);
+        decoder<typename BinaryCode::reader> dec;
+        uint32_t m = dec.decode(enc.bits().data(), out.data());
+        assert(m == n);
 
-    encoder<typename BinaryCode::writer> enc;
-    enc.encode(in.data(), n);
+        std::cout << "decoded " << m << " values" << std::endl;
+        std::cout << "total bits " << enc.num_bits() << std::endl;
+        std::cout << static_cast<double>(enc.num_bits()) / m << " bits x key"
+                  << std::endl;
 
-    std::vector<uint32_t> out(n);
-    decoder<typename BinaryCode::reader> dec;
-    uint32_t m = dec.decode(enc.bits().data(), out.data());
-    assert(m == n);
+        std::cout << "decoded:\n";
+        for (auto x : out) {
+            std::cout << x << " ";
+        }
+        std::cout << std::endl;
+    }
 
-    std::cout << "decoded " << m << " values" << std::endl;
-    std::cout << "total bits " << enc.num_bits() << std::endl;
-    std::cout << static_cast<double>(enc.num_bits()) / m << " bits x key"
-              << std::endl;
+    {
+        uint32_t n = in.size();
+        encoder<typename BinaryCode::writer> enc;
+        enc.encode(in.data(), n,
+                   false  // do not save n
+        );
+        std::vector<uint32_t> out(n);
+        decoder<typename BinaryCode::reader> dec(enc.bits().data());
+        uint32_t m = dec.decode(out.data(), n);
+        assert(m == n);
 
-    std::cout << "decoded:\n";
-    for (auto x : out) {
-        std::cout << x << " ";
+        std::cout << "decoded " << m << " values" << std::endl;
+        std::cout << "total bits " << enc.num_bits() << std::endl;
+        std::cout << static_cast<double>(enc.num_bits()) / m << " bits x key"
+                  << std::endl;
+
+        std::cout << "decoded:\n";
+        for (auto x : out) {
+            std::cout << x << " ";
+        }
+        std::cout << std::endl;
     }
-    std::cout << std::endl;
 }
 
 int main(int argc, char** argv) {