90 lines
3.4 KiB
C++
90 lines
3.4 KiB
C++
// Copyright 2010-2022 Google LLC
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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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// http://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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// Classes and function to convert floating point numbers to string so that no
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// information is lost (i.e. that we can make a round trip from double to string
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// and back to double without losing data).
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#ifndef OR_TOOLS_UTIL_FP_ROUNDTRIP_CONV_H_
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#define OR_TOOLS_UTIL_FP_ROUNDTRIP_CONV_H_
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#include <ostream>
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#include <string>
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#include "absl/base/attributes.h"
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#include "absl/status/statusor.h"
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#include "absl/strings/string_view.h"
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namespace operations_research {
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// True if the plateform supports `double` to std::to_chars().
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//
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// std::to_chars() for double is not yet supported on Emscripten, Android and
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// iOS; they only implement std::to_chars() for integers.
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ABSL_CONST_INIT extern const bool kStdToCharsDoubleIsSupported;
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// Formatter using std::to_chars() to print a `double` so that a round trip
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// conversion back to double will result in the same number (using
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// absl::from_chars()). One exception are NaNs that may not round trip
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// (i.e. multiple NaNs could end up being printed the same).
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//
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// Usage:
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//
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// const double x = ...;
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// LOG(INFO) << "x: " << RoundTripDoubleFormat(x);
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//
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// const std::string x_str =
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// absl::StrCat("x: ", RoundTripDoubleFormat::ToString(x));
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//
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// ASSIGN_OR_RETURN(const double y,
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// RoundTripDoubleFormat::Parse(x_str));
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//
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// Note that some operating systems do not support std::to_chars() for double
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// yet but only implement it for integers (see kStdToCharsDoubleIsSupported). On
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// those operating systems, a formatting equivalent to using "%.*g" with
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// max_digits10 precision is used.
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class RoundTripDoubleFormat {
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public:
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explicit RoundTripDoubleFormat(const double value) : value_(value) {}
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// Prints the formatted double to the provided stream.
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friend std::ostream& operator<<(std::ostream& out,
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const RoundTripDoubleFormat& format);
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// Returns a string with the provided double formatted.
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//
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// Prefer using operator<< when possible (with LOG(), StatusBuilder,
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// std::cout,...) since it avoids allocating a temporary string.
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//
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// PERFORMANCE: operator<< may be noticeably faster in some extreme cases,
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// especially in non-64bit platforms or when value is in (-∞, -1e+100] or in
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// [-1e-100, 0). This is because the string won't fit in
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// small-string-optimization buffer, and will thus need a heap memory
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// allocation which is slow.
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static std::string ToString(double value);
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// Parses the input string with absl::from_chars(), returning an error if the
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// input string does not start with a number or has extra characters after
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// it. It also fails if the number can't fit in a `double`.
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//
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// This function offers a round-trip from string printed/built by this
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// formatter.
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static absl::StatusOr<double> Parse(absl::string_view str_value);
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private:
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const double value_;
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};
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} // namespace operations_research
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#endif // OR_TOOLS_UTIL_FP_ROUNDTRIP_CONV_H_
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