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Diffstat (limited to 'absl/strings/internal/charconv_parse.h')
-rw-r--r-- | absl/strings/internal/charconv_parse.h | 98 |
1 files changed, 98 insertions, 0 deletions
diff --git a/absl/strings/internal/charconv_parse.h b/absl/strings/internal/charconv_parse.h new file mode 100644 index 00000000..41f4f40d --- /dev/null +++ b/absl/strings/internal/charconv_parse.h @@ -0,0 +1,98 @@ +// Copyright 2018 The Abseil Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. + +#ifndef ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_ +#define ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_ + +#include <cstdint> + +#include "absl/strings/charconv.h" + +namespace absl { +inline namespace lts_2018_06_20 { +namespace strings_internal { + +// Enum indicating whether a parsed float is a number or special value. +enum class FloatType { kNumber, kInfinity, kNan }; + +// The decomposed parts of a parsed `float` or `double`. +struct ParsedFloat { + // Representation of the parsed mantissa, with the decimal point adjusted to + // make it an integer. + // + // During decimal scanning, this contains 19 significant digits worth of + // mantissa value. If digits beyond this point are found, they + // are truncated, and if any of these dropped digits are nonzero, then + // `mantissa` is inexact, and the full mantissa is stored in [subrange_begin, + // subrange_end). + // + // During hexadecimal scanning, this contains 15 significant hex digits worth + // of mantissa value. Digits beyond this point are sticky -- they are + // truncated, but if any dropped digits are nonzero, the low bit of mantissa + // will be set. (This allows for precise rounding, and avoids the need + // to store the full mantissa in [subrange_begin, subrange_end).) + uint64_t mantissa = 0; + + // Floating point expontent. This reflects any decimal point adjustments and + // any truncated digits from the mantissa. The absolute value of the parsed + // number is represented by mantissa * (base ** exponent), where base==10 for + // decimal floats, and base==2 for hexadecimal floats. + int exponent = 0; + + // The literal exponent value scanned from the input, or 0 if none was + // present. This does not reflect any adjustments applied to mantissa. + int literal_exponent = 0; + + // The type of number scanned. + FloatType type = FloatType::kNumber; + + // When non-null, [subrange_begin, subrange_end) marks a range of characters + // that require further processing. The meaning is dependent on float type. + // If type == kNumber and this is set, this is a "wide input": the input + // mantissa contained more than 19 digits. The range contains the full + // mantissa. It plus `literal_exponent` need to be examined to find the best + // floating point match. + // If type == kNan and this is set, the range marks the contents of a + // matched parenthesized character region after the NaN. + const char* subrange_begin = nullptr; + const char* subrange_end = nullptr; + + // One-past-the-end of the successfully parsed region, or nullptr if no + // matching pattern was found. + const char* end = nullptr; +}; + +// Read the floating point number in the provided range, and populate +// ParsedFloat accordingly. +// +// format_flags is a bitmask value specifying what patterns this API will match. +// `scientific` and `fixed` are honored per std::from_chars rules +// ([utility.from.chars], C++17): if exactly one of these bits is set, then an +// exponent is required, or dislallowed, respectively. +// +// Template parameter `base` must be either 10 or 16. For base 16, a "0x" is +// *not* consumed. The `hex` bit from format_flags is ignored by ParseFloat. +template <int base> +ParsedFloat ParseFloat(const char* begin, const char* end, + absl::chars_format format_flags); + +extern template ParsedFloat ParseFloat<10>(const char* begin, const char* end, + absl::chars_format format_flags); +extern template ParsedFloat ParseFloat<16>(const char* begin, const char* end, + absl::chars_format format_flags); + +} // namespace strings_internal +} // inline namespace lts_2018_06_20 +} // namespace absl +#endif // ABSL_STRINGS_INTERNAL_CHARCONV_PARSE_H_ |