__cxx03/__charconv/traits.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //===----------------------------------------------------------------------===//
0009
0010 #ifndef _LIBCPP___CXX03___CHARCONV_TRAITS
0011 #define _LIBCPP___CXX03___CHARCONV_TRAITS
0012
0013 #include <__cxx03/__assert>
0014 #include <__cxx03/__bit/countl.h>
0015 #include <__cxx03/__charconv/tables.h>
0016 #include <__cxx03/__charconv/to_chars_base_10.h>
0017 #include <__cxx03/__config>
0018 #include <__cxx03/__type_traits/enable_if.h>
0019 #include <__cxx03/__type_traits/is_unsigned.h>
0020 #include <__cxx03/cstdint>
0021 #include <__cxx03/limits>
0022
0023 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0024 #  pragma GCC system_header
0025 #endif
0026
0027 _LIBCPP_PUSH_MACROS
0028 #include <__cxx03/__undef_macros>
0029
0030 _LIBCPP_BEGIN_NAMESPACE_STD
0031
0032 #if _LIBCPP_STD_VER >= 17
0033
0034 namespace __itoa {
0035
0036 template <typename _Tp, typename = void>
0037 struct _LIBCPP_HIDDEN __traits_base;
0038
0039 template <typename _Tp>
0040 struct _LIBCPP_HIDDEN __traits_base<_Tp, __enable_if_t<sizeof(_Tp) <= sizeof(uint32_t)>> {
0041   using type = uint32_t;
0042
0043   /// The width estimation using a log10 algorithm.
0044   ///
0045   /// The algorithm is based on
0046   /// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
0047   /// Instead of using IntegerLogBase2 it uses __libcpp_clz. Since that
0048   /// function requires its input to have at least one bit set the value of
0049   /// zero is set to one. This means the first element of the lookup table is
0050   /// zero.
0051   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI int __width(_Tp __v) {
0052     auto __t = (32 - std::__libcpp_clz(static_cast<type>(__v | 1))) * 1233 >> 12;
0053     return __t - (__v < __itoa::__pow10_32[__t]) + 1;
0054   }
0055
0056   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI char* __convert(char* __p, _Tp __v) {
0057     return __itoa::__base_10_u32(__p, __v);
0058   }
0059
0060   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI decltype(__pow10_32)& __pow() {
0061     return __itoa::__pow10_32;
0062   }
0063 };
0064
0065 template <typename _Tp>
0066 struct _LIBCPP_HIDDEN __traits_base<_Tp, __enable_if_t<sizeof(_Tp) == sizeof(uint64_t)>> {
0067   using type = uint64_t;
0068
0069   /// The width estimation using a log10 algorithm.
0070   ///
0071   /// The algorithm is based on
0072   /// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
0073   /// Instead of using IntegerLogBase2 it uses __libcpp_clz. Since that
0074   /// function requires its input to have at least one bit set the value of
0075   /// zero is set to one. This means the first element of the lookup table is
0076   /// zero.
0077   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI int __width(_Tp __v) {
0078     auto __t = (64 - std::__libcpp_clz(static_cast<type>(__v | 1))) * 1233 >> 12;
0079     return __t - (__v < __itoa::__pow10_64[__t]) + 1;
0080   }
0081
0082   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI char* __convert(char* __p, _Tp __v) {
0083     return __itoa::__base_10_u64(__p, __v);
0084   }
0085
0086   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI decltype(__pow10_64)& __pow() {
0087     return __itoa::__pow10_64;
0088   }
0089 };
0090
0091 #  ifndef _LIBCPP_HAS_NO_INT128
0092 template <typename _Tp>
0093 struct _LIBCPP_HIDDEN __traits_base<_Tp, __enable_if_t<sizeof(_Tp) == sizeof(__uint128_t)> > {
0094   using type = __uint128_t;
0095
0096   /// The width estimation using a log10 algorithm.
0097   ///
0098   /// The algorithm is based on
0099   /// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog10
0100   /// Instead of using IntegerLogBase2 it uses __libcpp_clz. Since that
0101   /// function requires its input to have at least one bit set the value of
0102   /// zero is set to one. This means the first element of the lookup table is
0103   /// zero.
0104   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI int __width(_Tp __v) {
0105     _LIBCPP_ASSERT_INTERNAL(
0106         __v > numeric_limits<uint64_t>::max(), "The optimizations for this algorithm fail when this isn't true.");
0107     // There's always a bit set in the upper 64-bits.
0108     auto __t = (128 - std::__libcpp_clz(static_cast<uint64_t>(__v >> 64))) * 1233 >> 12;
0109     _LIBCPP_ASSERT_INTERNAL(__t >= __itoa::__pow10_128_offset, "Index out of bounds");
0110     // __t is adjusted since the lookup table misses the lower entries.
0111     return __t - (__v < __itoa::__pow10_128[__t - __itoa::__pow10_128_offset]) + 1;
0112   }
0113
0114   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI char* __convert(char* __p, _Tp __v) {
0115     return __itoa::__base_10_u128(__p, __v);
0116   }
0117
0118   // TODO FMT This pow function should get an index.
0119   // By moving this to its own header it can be reused by the pow function in to_chars_base_10.
0120   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI decltype(__pow10_128)& __pow() {
0121     return __itoa::__pow10_128;
0122   }
0123 };
0124 #  endif
0125
0126 template <typename _Tp>
0127 inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool
0128 __mul_overflowed(unsigned char __a, _Tp __b, unsigned char& __r) {
0129   auto __c = __a * __b;
0130   __r      = __c;
0131   return __c > numeric_limits<unsigned char>::max();
0132 }
0133
0134 template <typename _Tp>
0135 inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool
0136 __mul_overflowed(unsigned short __a, _Tp __b, unsigned short& __r) {
0137   auto __c = __a * __b;
0138   __r      = __c;
0139   return __c > numeric_limits<unsigned short>::max();
0140 }
0141
0142 template <typename _Tp>
0143 inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI bool __mul_overflowed(_Tp __a, _Tp __b, _Tp& __r) {
0144   static_assert(is_unsigned<_Tp>::value, "");
0145   return __builtin_mul_overflow(__a, __b, &__r);
0146 }
0147
0148 template <typename _Tp, typename _Up>
0149 inline _LIBCPP_HIDE_FROM_ABI bool _LIBCPP_CONSTEXPR_SINCE_CXX23 __mul_overflowed(_Tp __a, _Up __b, _Tp& __r) {
0150   return __itoa::__mul_overflowed(__a, static_cast<_Tp>(__b), __r);
0151 }
0152
0153 template <typename _Tp>
0154 struct _LIBCPP_HIDDEN __traits : __traits_base<_Tp> {
0155   static constexpr int digits = numeric_limits<_Tp>::digits10 + 1;
0156   using __traits_base<_Tp>::__pow;
0157   using typename __traits_base<_Tp>::type;
0158
0159   // precondition: at least one non-zero character available
0160   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI char const*
0161   __read(char const* __p, char const* __ep, type& __a, type& __b) {
0162     type __cprod[digits];
0163     int __j = digits - 1;
0164     int __i = digits;
0165     do {
0166       if (*__p < '0' || *__p > '9')
0167         break;
0168       __cprod[--__i] = *__p++ - '0';
0169     } while (__p != __ep && __i != 0);
0170
0171     __a = __inner_product(__cprod + __i + 1, __cprod + __j, __pow() + 1, __cprod[__i]);
0172     if (__itoa::__mul_overflowed(__cprod[__j], __pow()[__j - __i], __b))
0173       --__p;
0174     return __p;
0175   }
0176
0177   template <typename _It1, typename _It2, class _Up>
0178   static _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI _Up
0179   __inner_product(_It1 __first1, _It1 __last1, _It2 __first2, _Up __init) {
0180     for (; __first1 < __last1; ++__first1, ++__first2)
0181       __init = __init + *__first1 * *__first2;
0182     return __init;
0183   }
0184 };
0185
0186 } // namespace __itoa
0187
0188 template <typename _Tp>
0189 inline _LIBCPP_CONSTEXPR_SINCE_CXX23 _LIBCPP_HIDE_FROM_ABI _Tp __complement(_Tp __x) {
0190   static_assert(is_unsigned<_Tp>::value, "cast to unsigned first");
0191   return _Tp(~__x + 1);
0192 }
0193
0194 #endif // _LIBCPP_STD_VER >= 17
0195
0196 _LIBCPP_END_NAMESPACE_STD
0197
0198 _LIBCPP_POP_MACROS
0199
0200 #endif // _LIBCPP___CXX03___CHARCONV_TRAITS