107 lines
3.4 KiB
C++
107 lines
3.4 KiB
C++
// Numeric conversions (to_string, to_chars) -*- C++ -*-
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// Copyright (C) 2017-2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file bits/charconv.h
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* This is an internal header file, included by other library headers.
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* Do not attempt to use it directly. @headername{charconv}
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*/
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#ifndef _GLIBCXX_CHARCONV_H
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#define _GLIBCXX_CHARCONV_H 1
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#pragma GCC system_header
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#if __cplusplus >= 201103L
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#include <type_traits>
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namespace std _GLIBCXX_VISIBILITY(default)
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{
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_GLIBCXX_BEGIN_NAMESPACE_VERSION
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namespace __detail
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{
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// Generic implementation for arbitrary bases.
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template<typename _Tp>
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_GLIBCXX14_CONSTEXPR unsigned
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__to_chars_len(_Tp __value, int __base = 10) noexcept
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{
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static_assert(is_integral<_Tp>::value, "implementation bug");
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static_assert(is_unsigned<_Tp>::value, "implementation bug");
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unsigned __n = 1;
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const unsigned __b2 = __base * __base;
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const unsigned __b3 = __b2 * __base;
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const unsigned long __b4 = __b3 * __base;
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for (;;)
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{
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if (__value < (unsigned)__base) return __n;
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if (__value < __b2) return __n + 1;
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if (__value < __b3) return __n + 2;
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if (__value < __b4) return __n + 3;
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__value /= __b4;
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__n += 4;
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}
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}
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// Write an unsigned integer value to the range [first,first+len).
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// The caller is required to provide a buffer of exactly the right size
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// (which can be determined by the __to_chars_len function).
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template<typename _Tp>
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void
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__to_chars_10_impl(char* __first, unsigned __len, _Tp __val) noexcept
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{
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static_assert(is_integral<_Tp>::value, "implementation bug");
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static_assert(is_unsigned<_Tp>::value, "implementation bug");
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static constexpr char __digits[201] =
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"0001020304050607080910111213141516171819"
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"2021222324252627282930313233343536373839"
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"4041424344454647484950515253545556575859"
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"6061626364656667686970717273747576777879"
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"8081828384858687888990919293949596979899";
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unsigned __pos = __len - 1;
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while (__val >= 100)
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{
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auto const __num = (__val % 100) * 2;
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__val /= 100;
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__first[__pos] = __digits[__num + 1];
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__first[__pos - 1] = __digits[__num];
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__pos -= 2;
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}
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if (__val >= 10)
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{
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auto const __num = __val * 2;
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__first[1] = __digits[__num + 1];
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__first[0] = __digits[__num];
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}
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else
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__first[0] = '0' + __val;
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}
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} // namespace __detail
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_GLIBCXX_END_NAMESPACE_VERSION
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} // namespace std
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#endif // C++11
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#endif // _GLIBCXX_CHARCONV_H
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