зеркало из https://github.com/mozilla/gecko-dev.git
42 строки
1.4 KiB
C++
42 строки
1.4 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
|
|
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
|
|
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
/* Implementations of FloatingPoint functions */
|
|
|
|
#include "mozilla/FloatingPoint.h"
|
|
|
|
#include <cfloat> // for FLT_MAX
|
|
|
|
namespace mozilla {
|
|
|
|
bool IsFloat32Representable(double aValue) {
|
|
// NaNs and infinities are representable.
|
|
if (!IsFinite(aValue)) {
|
|
return true;
|
|
}
|
|
|
|
// If it exceeds finite |float| range, casting to |double| is always undefined
|
|
// behavior per C++11 [conv.double]p1 last sentence.
|
|
if (Abs(aValue) > FLT_MAX) {
|
|
return false;
|
|
}
|
|
|
|
// But if it's within finite range, then either it's 1) an exact value and so
|
|
// representable, or 2) it's "between two adjacent destination values" and
|
|
// safe to cast to "an implementation-defined choice of either of those
|
|
// values".
|
|
auto valueAsFloat = static_cast<float>(aValue);
|
|
|
|
// Per [conv.fpprom] this never changes value.
|
|
auto valueAsFloatAsDouble = static_cast<double>(valueAsFloat);
|
|
|
|
// Finally, in 1) exact representable value equals exact representable value,
|
|
// or 2) *changed* value does not equal original value, ergo unrepresentable.
|
|
return valueAsFloatAsDouble == aValue;
|
|
}
|
|
|
|
} /* namespace mozilla */
|