charconv_parse.h (4326B)
1 // Copyright 2018 The Abseil Authors. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // https://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 #ifndef ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_ 16 #define ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_ 17 18 #include <cstdint> 19 20 #include "absl/base/config.h" 21 #include "absl/strings/charconv.h" 22 23 namespace absl { 24 ABSL_NAMESPACE_BEGIN 25 namespace strings_internal { 26 27 // Enum indicating whether a parsed float is a number or special value. 28 enum class FloatType { kNumber, kInfinity, kNan }; 29 30 // The decomposed parts of a parsed `float` or `double`. 31 struct ParsedFloat { 32 // Representation of the parsed mantissa, with the decimal point adjusted to 33 // make it an integer. 34 // 35 // During decimal scanning, this contains 19 significant digits worth of 36 // mantissa value. If digits beyond this point are found, they 37 // are truncated, and if any of these dropped digits are nonzero, then 38 // `mantissa` is inexact, and the full mantissa is stored in [subrange_begin, 39 // subrange_end). 40 // 41 // During hexadecimal scanning, this contains 15 significant hex digits worth 42 // of mantissa value. Digits beyond this point are sticky -- they are 43 // truncated, but if any dropped digits are nonzero, the low bit of mantissa 44 // will be set. (This allows for precise rounding, and avoids the need 45 // to store the full mantissa in [subrange_begin, subrange_end).) 46 uint64_t mantissa = 0; 47 48 // Floating point expontent. This reflects any decimal point adjustments and 49 // any truncated digits from the mantissa. The absolute value of the parsed 50 // number is represented by mantissa * (base ** exponent), where base==10 for 51 // decimal floats, and base==2 for hexadecimal floats. 52 int exponent = 0; 53 54 // The literal exponent value scanned from the input, or 0 if none was 55 // present. This does not reflect any adjustments applied to mantissa. 56 int literal_exponent = 0; 57 58 // The type of number scanned. 59 FloatType type = FloatType::kNumber; 60 61 // When non-null, [subrange_begin, subrange_end) marks a range of characters 62 // that require further processing. The meaning is dependent on float type. 63 // If type == kNumber and this is set, this is a "wide input": the input 64 // mantissa contained more than 19 digits. The range contains the full 65 // mantissa. It plus `literal_exponent` need to be examined to find the best 66 // floating point match. 67 // If type == kNan and this is set, the range marks the contents of a 68 // matched parenthesized character region after the NaN. 69 const char* subrange_begin = nullptr; 70 const char* subrange_end = nullptr; 71 72 // One-past-the-end of the successfully parsed region, or nullptr if no 73 // matching pattern was found. 74 const char* end = nullptr; 75 }; 76 77 // Read the floating point number in the provided range, and populate 78 // ParsedFloat accordingly. 79 // 80 // format_flags is a bitmask value specifying what patterns this API will match. 81 // `scientific` and `fixed` are honored per std::from_chars rules 82 // ([utility.from.chars], C++17): if exactly one of these bits is set, then an 83 // exponent is required, or dislallowed, respectively. 84 // 85 // Template parameter `base` must be either 10 or 16. For base 16, a "0x" is 86 // *not* consumed. The `hex` bit from format_flags is ignored by ParseFloat. 87 template <int base> 88 ParsedFloat ParseFloat(const char* begin, const char* end, 89 absl::chars_format format_flags); 90 91 extern template ParsedFloat ParseFloat<10>(const char* begin, const char* end, 92 absl::chars_format format_flags); 93 extern template ParsedFloat ParseFloat<16>(const char* begin, const char* end, 94 absl::chars_format format_flags); 95 96 } // namespace strings_internal 97 ABSL_NAMESPACE_END 98 } // namespace absl 99 #endif // ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_