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fix dumb bug in input randomiser, add basic double->string benchmarks
* input randomiser was feeding a constant value previously, now actually randomising * start to_string with the current method (sstream), an faster more correct version (sstream_cached), snprintf, and std::to_chars ** NOTE: only std::to_chars and sstream_cached are correct in the face of locales Run on (4 X 3500 MHz CPU s) CPU Caches: L1 Data 32K (x4) L1 Instruction 32K (x4) L2 Unified 262K (x4) L3 Unified 6291K (x1) ------------------------------------------------------------------------------------------------------------- Benchmark Time CPU Iterations ------------------------------------------------------------------------------------------------------------- RandFloatStrs/double_from_string_sstream 1012 ns 1001 ns 640000 RandFloatStrs/double_from_string_strtod 276 ns 276 ns 2488889 RandFloatStrs/double_from_string_strtod_fixed 312 ns 308 ns 2133333 RandFloatStrs/double_from_string_strtod_fixed_const_ref 307 ns 300 ns 2240000 RandFloatStrs/double_from_string_std_from_chars 194 ns 188 ns 3733333 RandFloatCommaStrs/double_from_string_strtod_fixed_comma_ref 315 ns 314 ns 2240000 RandFloatCommaStrs/double_from_string_strtod_fixed_comma_const_ref 306 ns 305 ns 2357895 RandFloats/string_from_double_sstream 1372 ns 1381 ns 497778 RandFloats/string_from_double_sstream_cached 1136 ns 1123 ns 640000 RandFloats/string_from_double_snprintf 536 ns 516 ns 1000000 RandFloats/string_from_double_std_to_chars 116 ns 115 ns 6400000
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,2 +1,151 @@ | ||
| // A core part of the xlsx serialisation routine is taking doubles from memory and stringifying them | ||
| // this has a few requirements | ||
| // - expect strings in the form 1234.56 (i.e. no thousands seperator, '.' used for the decimal seperator) | ||
| // - outputs up to 15 significant figures (excel only serialises numbers up to 15sf) | ||
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| #include "benchmark/benchmark.h" | ||
| #include <locale> | ||
| #include <random> | ||
| #include <sstream> | ||
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| namespace { | ||
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| // setup a large quantity of random doubles as strings | ||
| template <bool Decimal_Locale = true> | ||
| class RandomFloats : public benchmark::Fixture | ||
| { | ||
| static constexpr size_t Number_of_Elements = 1 << 20; | ||
| static_assert(Number_of_Elements > 1'000'000, "ensure a decent set of random values is generated"); | ||
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| std::vector<double> inputs; | ||
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| size_t index = 0; | ||
| const char *locale_str = nullptr; | ||
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| public: | ||
| void SetUp(const ::benchmark::State &state) | ||
| { | ||
| if (Decimal_Locale) | ||
| { | ||
| locale_str = setlocale(LC_ALL, "C"); | ||
| } | ||
| else | ||
| { | ||
| locale_str = setlocale(LC_ALL, "de-DE"); | ||
| } | ||
| std::random_device rd; // obtain a seed for the random number engine | ||
| std::mt19937 gen(rd()); | ||
| // doing full range is stupid (<double>::min/max()...), it just ends up generating very large numbers | ||
| // uniform is probably not the best distribution to use here, but it will do for now | ||
| std::uniform_real_distribution<double> dis(-1'000, 1'000); | ||
| // generate a large quantity of doubles to deserialise | ||
| inputs.reserve(Number_of_Elements); | ||
| for (int i = 0; i < Number_of_Elements; ++i) | ||
| { | ||
| double d = dis(gen); | ||
| inputs.push_back(d); | ||
| } | ||
| } | ||
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| void TearDown(const ::benchmark::State &state) | ||
| { | ||
| // restore locale | ||
| setlocale(LC_ALL, locale_str); | ||
| // gbench is keeping the fixtures alive somewhere, need to clear the data after use | ||
| inputs = std::vector<double>{}; | ||
| } | ||
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| double &get_rand() | ||
| { | ||
| return inputs[++index & (Number_of_Elements - 1)]; | ||
| } | ||
| }; | ||
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| /// Takes in a double and outputs a string form of that number which will | ||
| /// serialise and deserialise without loss of precision | ||
| std::string serialize_number_to_string(double num) | ||
| { | ||
| // more digits and excel won't match | ||
| constexpr int Excel_Digit_Precision = 15; //sf | ||
| std::stringstream ss; | ||
| ss.precision(Excel_Digit_Precision); | ||
| ss << num; | ||
| return ss.str(); | ||
| } | ||
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| class number_serialiser | ||
| { | ||
| static constexpr int Excel_Digit_Precision = 15; //sf | ||
| std::ostringstream ss; | ||
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| public: | ||
| explicit number_serialiser() | ||
| { | ||
| ss.precision(Excel_Digit_Precision); | ||
| ss.imbue(std::locale("C")); | ||
| } | ||
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| std::string serialise(double d) | ||
| { | ||
| ss.str(""); // reset string buffer | ||
| ss.clear(); // reset any error flags | ||
| ss << d; | ||
| return ss.str(); | ||
| } | ||
| }; | ||
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| using RandFloats = RandomFloats<true>; | ||
| } // namespace | ||
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| BENCHMARK_F(RandFloats, string_from_double_sstream) | ||
| (benchmark::State &state) | ||
| { | ||
| while (state.KeepRunning()) | ||
| { | ||
| benchmark::DoNotOptimize( | ||
| serialize_number_to_string(get_rand())); | ||
| } | ||
| } | ||
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| BENCHMARK_F(RandFloats, string_from_double_sstream_cached) | ||
| (benchmark::State &state) | ||
| { | ||
| number_serialiser ser; | ||
| while (state.KeepRunning()) | ||
| { | ||
| benchmark::DoNotOptimize( | ||
| ser.serialise(get_rand())); | ||
| } | ||
| } | ||
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| BENCHMARK_F(RandFloats, string_from_double_snprintf) | ||
| (benchmark::State &state) | ||
| { | ||
| while (state.KeepRunning()) | ||
| { | ||
| char buf[16]; | ||
| int len = snprintf(buf, sizeof(buf), "%16f", get_rand()); | ||
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| benchmark::DoNotOptimize( | ||
| std::string(buf, len)); | ||
| } | ||
| } | ||
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| // locale names are different between OS's, and std::from_chars is only complete in MSVC | ||
| #ifdef _MSC_VER | ||
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| #include <charconv> | ||
| BENCHMARK_F(RandFloats, string_from_double_std_to_chars) | ||
| (benchmark::State &state) | ||
| { | ||
| while (state.KeepRunning()) | ||
| { | ||
| char buf[16]; | ||
| std::to_chars_result result = std::to_chars(buf, buf + std::size(buf), get_rand()); | ||
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| benchmark::DoNotOptimize( | ||
| std::string(buf, result.ptr)); | ||
| } | ||
| } | ||
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| #endif |
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