charconv_parse.h
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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/strings/charconv.h"
21 
22 namespace absl {
23 namespace strings_internal {
24 
25 // Enum indicating whether a parsed float is a number or special value.
26 enum class FloatType { kNumber, kInfinity, kNan };
27 
28 // The decomposed parts of a parsed `float` or `double`.
29 struct ParsedFloat {
30  // Representation of the parsed mantissa, with the decimal point adjusted to
31  // make it an integer.
32  //
33  // During decimal scanning, this contains 19 significant digits worth of
34  // mantissa value. If digits beyond this point are found, they
35  // are truncated, and if any of these dropped digits are nonzero, then
36  // `mantissa` is inexact, and the full mantissa is stored in [subrange_begin,
37  // subrange_end).
38  //
39  // During hexadecimal scanning, this contains 15 significant hex digits worth
40  // of mantissa value. Digits beyond this point are sticky -- they are
41  // truncated, but if any dropped digits are nonzero, the low bit of mantissa
42  // will be set. (This allows for precise rounding, and avoids the need
43  // to store the full mantissa in [subrange_begin, subrange_end).)
44  uint64_t mantissa = 0;
45 
46  // Floating point expontent. This reflects any decimal point adjustments and
47  // any truncated digits from the mantissa. The absolute value of the parsed
48  // number is represented by mantissa * (base ** exponent), where base==10 for
49  // decimal floats, and base==2 for hexadecimal floats.
50  int exponent = 0;
51 
52  // The literal exponent value scanned from the input, or 0 if none was
53  // present. This does not reflect any adjustments applied to mantissa.
54  int literal_exponent = 0;
55 
56  // The type of number scanned.
58 
59  // When non-null, [subrange_begin, subrange_end) marks a range of characters
60  // that require further processing. The meaning is dependent on float type.
61  // If type == kNumber and this is set, this is a "wide input": the input
62  // mantissa contained more than 19 digits. The range contains the full
63  // mantissa. It plus `literal_exponent` need to be examined to find the best
64  // floating point match.
65  // If type == kNan and this is set, the range marks the contents of a
66  // matched parenthesized character region after the NaN.
67  const char* subrange_begin = nullptr;
68  const char* subrange_end = nullptr;
69 
70  // One-past-the-end of the successfully parsed region, or nullptr if no
71  // matching pattern was found.
72  const char* end = nullptr;
73 };
74 
75 // Read the floating point number in the provided range, and populate
76 // ParsedFloat accordingly.
77 //
78 // format_flags is a bitmask value specifying what patterns this API will match.
79 // `scientific` and `fixed` are honored per std::from_chars rules
80 // ([utility.from.chars], C++17): if exactly one of these bits is set, then an
81 // exponent is required, or dislallowed, respectively.
82 //
83 // Template parameter `base` must be either 10 or 16. For base 16, a "0x" is
84 // *not* consumed. The `hex` bit from format_flags is ignored by ParseFloat.
85 template <int base>
86 ParsedFloat ParseFloat(const char* begin, const char* end,
87  absl::chars_format format_flags);
88 
89 extern template ParsedFloat ParseFloat<10>(const char* begin, const char* end,
90  absl::chars_format format_flags);
91 extern template ParsedFloat ParseFloat<16>(const char* begin, const char* end,
92  absl::chars_format format_flags);
93 
94 } // namespace strings_internal
95 } // namespace absl
96 #endif // ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_
char * begin
uint64_t mantissa
Definition: charconv.cc:238
char * end
template ParsedFloat ParseFloat< 10 >(const char *begin, const char *end, chars_format format_flags)
Definition: algorithm.h:29
template ParsedFloat ParseFloat< 16 >(const char *begin, const char *end, chars_format format_flags)
strings_internal::ParsedFloat ParseFloat(const char *begin, const char *end, chars_format format_flags)
int exponent
Definition: charconv.cc:239
chars_format
Definition: charconv.h:26


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autogenerated on Wed Jun 19 2019 19:19:56