102 lines
3.1 KiB
C++
102 lines
3.1 KiB
C++
/*
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* Copyright 2021 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <cassert>
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#include <charconv>
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#include <limits>
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#include <string>
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#include <string_view>
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#include <type_traits>
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namespace android::ftl {
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enum class Radix { kBin = 2, kDec = 10, kHex = 16 };
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template <typename T>
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struct to_chars_length {
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static_assert(std::is_integral_v<T>);
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// Maximum binary digits, plus minus sign and radix prefix.
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static constexpr std::size_t value = std::numeric_limits<std::make_unsigned_t<T>>::digits + 3;
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};
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template <typename T>
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constexpr std::size_t to_chars_length_v = to_chars_length<T>::value;
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template <typename T = std::int64_t>
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using to_chars_buffer_t = char[to_chars_length_v<T>];
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// Lightweight (not allocating nor sprintf-based) alternative to std::to_string for integers, with
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// optional radix. See also ftl::to_string below.
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//
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// ftl::to_chars_buffer_t<> buffer;
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//
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// assert(ftl::to_chars(buffer, 123u) == "123");
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// assert(ftl::to_chars(buffer, -42, ftl::Radix::kBin) == "-0b101010");
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// assert(ftl::to_chars(buffer, 0xcafe, ftl::Radix::kHex) == "0xcafe");
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// assert(ftl::to_chars(buffer, '*', ftl::Radix::kHex) == "0x2a");
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//
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template <typename T, std::size_t N>
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std::string_view to_chars(char (&buffer)[N], T v, Radix radix = Radix::kDec) {
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static_assert(N >= to_chars_length_v<T>);
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auto begin = buffer + 2;
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const auto [end, err] = std::to_chars(begin, buffer + N, v, static_cast<int>(radix));
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assert(err == std::errc());
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if (radix == Radix::kDec) {
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// TODO: Replace with {begin, end} in C++20.
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return {begin, static_cast<std::size_t>(end - begin)};
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}
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const auto prefix = radix == Radix::kBin ? 'b' : 'x';
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if constexpr (std::is_unsigned_v<T>) {
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buffer[0] = '0';
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buffer[1] = prefix;
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} else {
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if (*begin == '-') {
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*buffer = '-';
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} else {
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--begin;
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}
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*begin-- = prefix;
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*begin = '0';
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}
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// TODO: Replace with {buffer, end} in C++20.
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return {buffer, static_cast<std::size_t>(end - buffer)};
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}
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// Lightweight (not sprintf-based) alternative to std::to_string for integers, with optional radix.
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//
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// assert(ftl::to_string(123u) == "123");
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// assert(ftl::to_string(-42, ftl::Radix::kBin) == "-0b101010");
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// assert(ftl::to_string(0xcafe, ftl::Radix::kHex) == "0xcafe");
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// assert(ftl::to_string('*', ftl::Radix::kHex) == "0x2a");
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//
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template <typename T>
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inline std::string to_string(T v, Radix radix = Radix::kDec) {
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to_chars_buffer_t<T> buffer;
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return std::string(to_chars(buffer, v, radix));
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}
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std::string to_string(bool) = delete;
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std::string to_string(bool, Radix) = delete;
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} // namespace android::ftl
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