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9393060f90
While working on D70631, Microsoft's unit tests discovered an issue. Our `std::to_chars` implementation for bases != 10 uses the range `[first,last)` as temporary buffer. This violates the contract for to_chars: [charconv.to.chars]/1 http://eel.is/c++draft/charconv#to.chars-1 `to_chars_result to_chars(char* first, char* last, see below value, int base = 10);` "If the member ec of the return value is such that the value is equal to the value of a value-initialized errc, the conversion was successful and the member ptr is the one-past-the-end pointer of the characters written." Our implementation modifies the range `[member ptr, last)`, which causes Microsoft's test to fail. Their test verifies the buffer `[member ptr, last)` is unchanged. (The test is only done when the conversion is successful.) While looking at the code I noticed the performance for bases != 10 also is suboptimal. This is tracked in D97705. This patch fixes the issue and adds a benchmark. This benchmark will be used as baseline for D97705. Reviewed By: #libc, Quuxplusone, zoecarver Differential Revision: https://reviews.llvm.org/D100722
59 lines
2.0 KiB
C++
59 lines
2.0 KiB
C++
//===----------------------------------------------------------------------===//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#include <array>
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#include <charconv>
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#include <random>
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#include "benchmark/benchmark.h"
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#include "test_macros.h"
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static const std::array<unsigned, 1000> input = [] {
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std::mt19937 generator;
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std::uniform_int_distribution<unsigned> distribution(0, std::numeric_limits<unsigned>::max());
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std::array<unsigned, 1000> result;
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std::generate_n(result.begin(), result.size(), [&] { return distribution(generator); });
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return result;
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}();
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static void BM_to_chars_good(benchmark::State& state) {
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char buffer[128];
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int base = state.range(0);
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while (state.KeepRunningBatch(input.size()))
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for (auto value : input)
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benchmark::DoNotOptimize(std::to_chars(buffer, &buffer[128], value, base));
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}
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BENCHMARK(BM_to_chars_good)->DenseRange(2, 36, 1);
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static void BM_to_chars_bad(benchmark::State& state) {
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char buffer[128];
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int base = state.range(0);
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struct sample {
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unsigned size;
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unsigned value;
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};
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std::array<sample, 1000> data;
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// Assume the failure occurs, on average, halfway during the conversion.
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std::transform(input.begin(), input.end(), data.begin(), [&](unsigned value) {
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std::to_chars_result result = std::to_chars(buffer, &buffer[128], value, base);
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return sample{unsigned((result.ptr - buffer) / 2), value};
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});
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while (state.KeepRunningBatch(data.size()))
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for (auto element : data)
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benchmark::DoNotOptimize(std::to_chars(buffer, &buffer[element.size], element.value, base));
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}
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BENCHMARK(BM_to_chars_bad)->DenseRange(2, 36, 1);
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int main(int argc, char** argv) {
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benchmark::Initialize(&argc, argv);
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if (benchmark::ReportUnrecognizedArguments(argc, argv))
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return 1;
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benchmark::RunSpecifiedBenchmarks();
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}
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