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