add cifar-10 loader

cifar-10.hpp

+#ifndef __CIFAR10_HPP__
+#define __CIFAR10_HPP__
+
+#include <fstream>
+#include <vector>
+#include <tuple>
+#include <stdexcept>
+
+namespace{
+namespace mtk{
+constexpr std::size_t CIFAR_10_DIM = 32;
+using label_t = int;
+using image_t = std::vector<unsigned int>;
+using sample_t = std::tuple<image_t, label_t>;
+std::vector<sample_t> load_cifar_10(const std::string& filename) {
+	std::ifstream ifs(filename);
+	if(!ifs){
+		throw std::runtime_error("No such file : " + filename);
+	}
+
+	// compute file size
+	ifs.seekg(0, std::fstream::end);
+	const auto end_pos = ifs.tellg();
+	ifs.clear();
+	ifs.seekg(0, std::fstream::beg);
+	const auto begin_pos = ifs.tellg();
+
+	// validate size
+	if((end_pos - begin_pos) % (1 + CIFAR_10_DIM * CIFAR_10_DIM * 3) != 0){
+		throw std::runtime_error("Invalid data size");
+	}
+	const std::size_t sample_size = (end_pos - begin_pos) / (1 + CIFAR_10_DIM * CIFAR_10_DIM * 3);
+
+	// load sample data
+	std::vector<sample_t> samples;
+	for(auto i = decltype(sample_size)(0); i < sample_size; i++){
+		label_t label;
+		image_t image(CIFAR_10_DIM * CIFAR_10_DIM);
+
+		// load label
+		ifs.read((char*)&label, 1);
+
+		// load image data
+		for(int c = 2; c >= 0; c--){
+			for(auto y = decltype(CIFAR_10_DIM)(0); y < CIFAR_10_DIM; y++){
+				for(auto x = decltype(CIFAR_10_DIM)(0); x < CIFAR_10_DIM; x++){
+					unsigned int byte;
+					ifs.read((char*)&byte, 1);
+					image[x + y * CIFAR_10_DIM] |= (byte << (8 * c));
+				}
+			}
+		}
+		samples.push_back(std::make_tuple(image, label));
+	}
+	return samples;
+}
+}
+}
+
+#endif