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