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/* -*- 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
/* 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 (!std::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 */