libcxx/include/__format/format_string.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___FORMAT_FORMAT_STRING_H
  11 #define _LIBCPP___FORMAT_FORMAT_STRING_H
  12
  13 #include <__assert>
  14 #include <__config>
  15 #include <__format/format_error.h>
  16 #include <__iterator/concepts.h>
  17 #include <__iterator/iterator_traits.h> // iter_value_t
  18 #include <cstddef>
  19 #include <cstdint>
  20
  21 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  22 #  pragma GCC system_header
  23 #endif
  24
  25 _LIBCPP_BEGIN_NAMESPACE_STD
  26
  27 #if _LIBCPP_STD_VER >= 20
  28
  29 namespace __format {
  30
  31 template <contiguous_iterator _Iterator>
  32 struct _LIBCPP_TEMPLATE_VIS __parse_number_result {
  33   _Iterator __last;
  34   uint32_t __value;
  35 };
  36
  37 template <contiguous_iterator _Iterator>
  38 __parse_number_result(_Iterator, uint32_t) -> __parse_number_result<_Iterator>;
  39
  40 template <contiguous_iterator _Iterator>
  41 _LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
  42 __parse_number(_Iterator __begin, _Iterator __end);
  43
  44 /**
  45  * The maximum value of a numeric argument.
  46  *
  47  * This is used for:
  48  * * arg-id
  49  * * width as value or arg-id.
  50  * * precision as value or arg-id.
  51  *
  52  * The value is compatible with the maximum formatting width and precision
  53  * using the `%*` syntax on a 32-bit system.
  54  */
  55 inline constexpr uint32_t __number_max = INT32_MAX;
  56
  57 namespace __detail {
  58 template <contiguous_iterator _Iterator>
  59 _LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
  60 __parse_zero(_Iterator __begin, _Iterator, auto& __parse_ctx) {
  61   __parse_ctx.check_arg_id(0);
  62   return {++__begin, 0}; // can never be larger than the maximum.
  63 }
  64
  65 template <contiguous_iterator _Iterator>
  66 _LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
  67 __parse_automatic(_Iterator __begin, _Iterator, auto& __parse_ctx) {
  68   size_t __value = __parse_ctx.next_arg_id();
  69   _LIBCPP_ASSERT_UNCATEGORIZED(
  70       __value <= __number_max,
  71       "Compilers don't support this number of arguments");
  72
  73   return {__begin, uint32_t(__value)};
  74 }
  75
  76 template <contiguous_iterator _Iterator>
  77 _LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
  78 __parse_manual(_Iterator __begin, _Iterator __end, auto& __parse_ctx) {
  79   __parse_number_result<_Iterator> __r = __format::__parse_number(__begin, __end);
  80   __parse_ctx.check_arg_id(__r.__value);
  81   return __r;
  82 }
  83
  84 } // namespace __detail
  85
  86 /**
  87  * Parses a number.
  88  *
  89  * The number is used for the 31-bit values @em width and @em precision. This
  90  * allows a maximum value of 2147483647.
  91  */
  92 template <contiguous_iterator _Iterator>
  93 _LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
  94 __parse_number(_Iterator __begin, _Iterator __end_input) {
  95   using _CharT = iter_value_t<_Iterator>;
  96   static_assert(__format::__number_max == INT32_MAX,
  97                 "The algorithm is implemented based on this value.");
  98   /*
  99    * Limit the input to 9 digits, otherwise we need two checks during every
 100    * iteration:
 101    * - Are we at the end of the input?
 102    * - Does the value exceed width of an uint32_t? (Switching to uint64_t would
 103    *   have the same issue, but with a higher maximum.)
 104    */
 105   _Iterator __end = __end_input - __begin > 9 ? __begin + 9 : __end_input;
 106   uint32_t __value = *__begin - _CharT('0');
 107   while (++__begin != __end) {
 108     if (*__begin < _CharT('0') || *__begin > _CharT('9'))
 109       return {__begin, __value};
 110
 111     __value = __value * 10 + *__begin - _CharT('0');
 112   }
 113
 114   if (__begin != __end_input && *__begin >= _CharT('0') &&
 115       *__begin <= _CharT('9')) {
 116
 117     /*
 118      * There are more than 9 digits, do additional validations:
 119      * - Does the 10th digit exceed the maximum allowed value?
 120      * - Are there more than 10 digits?
 121      * (More than 10 digits always overflows the maximum.)
 122      */
 123     uint64_t __v = uint64_t(__value) * 10 + *__begin++ - _CharT('0');
 124     if (__v > __number_max ||
 125         (__begin != __end_input && *__begin >= _CharT('0') &&
 126          *__begin <= _CharT('9')))
 127       std::__throw_format_error("The numeric value of the format specifier is too large");
 128
 129     __value = __v;
 130   }
 131
 132   return {__begin, __value};
 133 }
 134
 135 /**
 136  * Multiplexer for all parse functions.
 137  *
 138  * The parser will return a pointer beyond the last consumed character. This
 139  * should be the closing '}' of the arg-id.
 140  */
 141 template <contiguous_iterator _Iterator>
 142 _LIBCPP_HIDE_FROM_ABI constexpr __parse_number_result<_Iterator>
 143 __parse_arg_id(_Iterator __begin, _Iterator __end, auto& __parse_ctx) {
 144   using _CharT = iter_value_t<_Iterator>;
 145   switch (*__begin) {
 146   case _CharT('0'):
 147     return __detail::__parse_zero(__begin, __end, __parse_ctx);
 148
 149   case _CharT(':'):
 150     // This case is conditionally valid. It's allowed in an arg-id in the
 151     // replacement-field, but not in the std-format-spec. The caller can
 152     // provide a better diagnostic, so accept it here unconditionally.
 153   case _CharT('}'):
 154     return __detail::__parse_automatic(__begin, __end, __parse_ctx);
 155   }
 156   if (*__begin < _CharT('0') || *__begin > _CharT('9'))
 157     std::__throw_format_error("The argument index starts with an invalid character");
 158
 159   return __detail::__parse_manual(__begin, __end, __parse_ctx);
 160 }
 161
 162 } // namespace __format
 163
 164 #endif //_LIBCPP_STD_VER >= 20
 165
 166 _LIBCPP_END_NAMESPACE_STD
 167
 168 #endif // _LIBCPP___FORMAT_FORMAT_STRING_H