Trying with a smaller lookup, still slower than std::to_string

include/duckhandy/implem/int_conv.hpp

@@ -159,14 +159,13 @@ namespace dhandy {
 				using RetType = RevArray<I, 10, Tr>;
 				using Num = implem::NumberAdaptation<I, 10>;
 
-				const constexpr char lookup[200] = {
-					0,0,0,1,0,2,0,3,0,4,0,5,0,6,0,7,0,8,0,9,1,0,1,1,1,2,1,3,1,4,
-					1,5,1,6,1,7,1,8,1,9,2,0,2,1,2,2,2,3,2,4,2,5,2,6,2,7,2,8,2,9,
-					3,0,3,1,3,2,3,3,3,4,3,5,3,6,3,7,3,8,3,9,4,0,4,1,4,2,4,3,4,4,
-					4,5,4,6,4,7,4,8,4,9,5,0,5,1,5,2,5,3,5,4,5,5,5,6,5,7,5,8,5,9,
-					6,0,6,1,6,2,6,3,6,4,6,5,6,6,6,7,6,8,6,9,7,0,7,1,7,2,7,3,7,4,
-					7,5,7,6,7,7,7,8,7,9,8,0,8,1,8,2,8,3,8,4,8,5,8,6,8,7,8,8,8,9,
-					9,0,9,1,9,2,9,3,9,4,9,5,9,6,9,7,9,8,9,9
+				//How to build this lookup: 1) write numbers 0, 10, 20..., 90
+				//in binary; 2) take the lowest 5 bits, div by 2 and write as
+				//decimal; 3) divide by 2; 4) the result is the position in the
+				//below array that should be filled in with the leading digit
+				//from the original 0-90 number
+				constexpr const char lookup[16] = {
+					 0, 0, 0, 7, 4, 1, 0, 0, 8, 5, 2, 0, 0, 9, 6, 3
 				};
 				const bool was_negative = implem::is_negative<I, 10>(in);
 
@@ -176,18 +175,21 @@ namespace dhandy {
 				arr.push_front(Tr::NullChar);
 				in = Num::abs(in);
 				while (in >= static_cast<I>(100)) {
-					const auto index = (in % 100) * 2;
-					arr.push_front(Tr::to_digit(static_cast<int>(lookup[index + 1])));
-					arr.push_front(Tr::to_digit(static_cast<int>(lookup[index + 0])));
+					const auto last_two = in % 100;
+					const auto digit_low = in % 10;
 					in = static_cast<I>(in / static_cast<I>(100));
+					const auto digit_high = lookup[((last_two - digit_low) >> 1) & 0xF];
+					arr.push_front(Tr::to_digit(static_cast<int>(digit_low)));
+					arr.push_front(Tr::to_digit(static_cast<int>(digit_high)));
 				};
 				if (in < static_cast<I>(10)) {
 					arr.push_front(Tr::to_digit(static_cast<int>(in)));
 				}
 				else {
-					const auto index = in * 2;
-					arr.push_front(Tr::to_digit(static_cast<int>(lookup[index + 1])));
-					arr.push_front(Tr::to_digit(static_cast<int>(lookup[index + 0])));
+					const auto digit_low = in % 10;
+					const auto digit_high = lookup[((in - digit_low) >> 1) & 0xF];
+					arr.push_front(Tr::to_digit(static_cast<int>(digit_low)));
+					arr.push_front(Tr::to_digit(static_cast<int>(digit_high)));
 				}
 				if (was_negative)
 					arr.push_front(Tr::Minus);

speed_test_int_conv.cpp

@@ -0,0 +1,56 @@
+#include "duckhandy/int_conv.hpp"
+#include <iostream>
+#include <random>
+#include <chrono>
+#include <vector>
+#include <string>
+#include <algorithm>
+#include <ctime>
+
+namespace {
+template <typename Conv>
+void run_with_timing (
+	const std::string& test_name,
+	const std::vector<unsigned int>& src,
+	std::vector<std::string>& dst,
+	Conv&& conv_func
+) {
+	dst.clear();
+	dst.resize(src.size());
+	std::cout << test_name << "...\n";
+	const std::size_t count = src.size();
+
+	const auto t0 = std::chrono::high_resolution_clock::now();
+	for (std::size_t z = 0; z < count; ++z) {
+		dst[z] = conv_func(src[z]);
+	}
+	const auto t1 = std::chrono::high_resolution_clock::now();
+
+	std::chrono::duration<double> duration = t1 - t0;
+	std::cout << count << " conversions completed in " << duration.count() << " seconds\n";
+}
+} //unnamed namespace
+
+int main() {
+	using dhandy::int_conv;
+	constexpr const std::size_t count = 50'000'000;
+
+	std::vector<unsigned int> nums;
+	std::vector<std::string> strings;
+	std::mt19937 gen;
+
+	std::cout << "Setting up data...\n";
+
+	nums.resize(count);
+	strings.reserve(count);
+	gen.seed(std::time(nullptr));
+
+	std::cout << "Generating " << count << " random values...\n";
+	std::generate(nums.begin(), nums.end(), gen);
+
+	run_with_timing("Conversions with std::to_string", nums, strings, [](unsigned int n) { return std::to_string(n); });
+	run_with_timing("AryConversion with dhandy::int_conv", nums, strings, [](unsigned int n) { return int_conv<std::string>(n); });
+
+	std::cout << "All done, bye!\n";
+	return 0;
+}