Added a second way to save an image

include/utilities.hpp

@@ -1,11 +1,19 @@
 #pragma once
 
 #include <string>
+#include <chrono>
 
 inline bool is_pow_of_two(int n){
 	return (n & (n - 1)) == 0;
 }
 
+// calculates integer 2-log such that:
+// 2^(two_log(x)) >= x > 2^(two_log(x) - 1)
+unsigned int two_log(unsigned int x){
+	if(x <= 1) return 0;
+	return 8*sizeof(unsigned int) - __builtin_clz(x-1);
+}
+
 inline std::string human_string(int n){
 	static const std::string names [] = {"", "K", "M", "G"};
 	int i = 0;
@@ -22,3 +30,23 @@ inline std::string field(std::string const & str){
 	auto add = length - str.size();
 	return str + ":" + std::string(add, ' ') + "\t";
 }
+
+struct timer{
+	typedef std::chrono::high_resolution_clock clock;
+	typedef std::chrono::time_point<clock> time;
+	typedef std::chrono::duration<double> seconds;
+
+	std::string name;
+	time begin;
+
+	timer(std::string name)
+	: name(name)
+	, begin(clock::now())
+	{}
+
+	~timer(){
+		time end = clock::now();
+		seconds elapsed = end - begin;
+		std::cout << name << "\t" << elapsed.count() << std::endl;
+	}
+};

wavelet/compressed_image.hpp

@@ -43,6 +43,9 @@ namespace jcmp {
 		}
 	};
 
+	// Way of writing does not matter for performance
+	// timings: http://i.imgur.com/cskC43O.png (300 points per method)
+	// It's not surprising as filebuf is already a buffer
 	inline void write_to_file(image const & image, std::string filename){
 		std::filebuf file;
 		file.open(filename, std::ios_base::out|std::ios_base::trunc);
@@ -50,6 +53,23 @@ namespace jcmp {
 		file.sputn(reinterpret_cast<const char*>(image.data.data()), image.data.size() * sizeof(coefficient));
 	}
 
+	// Assumes Iterator points to a coefficient]
+	// length in header is not used
+	template <typename Iterator>
+	inline void write_to_file(header h, Iterator begin, Iterator end, std::string filename){
+		h.length = 0;
+		std::filebuf file;
+		file.open(filename, std::ios_base::out|std::ios_base::trunc);
+		file.sputn(reinterpret_cast<const char*>(&h), sizeof(header));
+		while(begin != end){
+			file.sputn(reinterpret_cast<const char*>(&*begin++), sizeof(coefficient));
+			h.length++;
+		}
+		// http://stackoverflow.com/questions/2530274/how-to-overwrite-only-part-of-a-file-in-c
+		file.pubseekpos(0);
+		file.sputn(reinterpret_cast<const char*>(&h), sizeof(header));
+	}
+
 	inline image read_from_file(std::string const& filename){
 		std::filebuf file;
 		file.open(filename, std::ios_base::in);
@@ -60,5 +80,4 @@ namespace jcmp {
 		file.sgetn(reinterpret_cast<char*>(image.data.data()), image.data.size() * sizeof(coefficient));
 		return image;
 	}
-
 }

wavelet/compressed_image_test.cpp

@@ -1,4 +1,5 @@
 #include <includes.hpp>
+#include <utilities.hpp>
 
 #include "compressed_image.hpp"
 namespace jcmp{
@@ -21,13 +22,21 @@ struct gen{
 	}
 };
 
-int main(){
+void test_correctness(){
 	const int w = 1024, h = 512;
-	srand(time(0));
-
 	std::vector<jcmp::coefficient> v(w*h / 100);
 	std::generate(v.begin(), v.end(), gen{w, 0, 0});
 
+	{	// iterator method
+		jcmp::write_to_file({w, h}, v.begin(), v.end(), "test.jcmp");
+		auto j = jcmp::read_from_file("test.jcmp");
+
+		assert(w == j.header.width);
+		assert(h == j.header.height);
+		assert(v == j.data);
+	}
+
+	{	// copy method
 		jcmp::image i(w, h, std::move(v));
 
 		jcmp::write_to_file(i, "test.jcmp");
@@ -35,8 +44,41 @@ int main(){
 
 		assert(w == j.header.width);
 		assert(h == j.header.height);
-	assert(i.data.size() == j.data.size());
 		assert(i.data == j.data);
+	}
+}
+
+void test_speed(){
+	const int w = 4000, h = 8000;
+	std::vector<jcmp::coefficient> input(w*h / 20);
+	std::generate(input.begin(), input.end(), gen{w, 0, 0});
 
+	for(int i = 0; i < 10; ++i){
+		{	timer t("stream");
+			jcmp::write_to_file({w, h}, input.begin(), input.end(), "stream.jcmp");
+		}
+
+		std::vector<jcmp::coefficient> copy(w*h / 20);
+		std::copy(input.begin(), input.end(), copy.begin());
+
+		{	timer t("move");
+			jcmp::image i(w, h, std::move(copy));
+			jcmp::write_to_file(i, "move.jcmp");
+		}
+
+		{	timer t("copy");
+			jcmp::image i(w, h, input);
+			jcmp::write_to_file(i, "copy.jcmp");
+		}
+	}
+}
+
+int main(){
+	srand(time(0));
+
+	test_correctness();
 	std::cout << "Test succeeded" << std::endl;
+
+	test_speed();
+	std::cout << "Test completed" << std::endl;
 }