FloatingPoint.cpp (1460B)
1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ 2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */ 3 /* This Source Code Form is subject to the terms of the Mozilla Public 4 * License, v. 2.0. If a copy of the MPL was not distributed with this 5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ 6 7 /* Implementations of FloatingPoint functions */ 8 9 #include "mozilla/FloatingPoint.h" 10 11 #include <cfloat> // for FLT_MAX 12 #include <cmath> 13 14 namespace mozilla { 15 16 bool IsFloat32Representable(double aValue) { 17 // NaNs and infinities are representable. 18 if (!std::isfinite(aValue)) { 19 return true; 20 } 21 22 // If it exceeds finite |float| range, casting to |double| is always undefined 23 // behavior per C++11 [conv.double]p1 last sentence. 24 if (Abs(aValue) > FLT_MAX) { 25 return false; 26 } 27 28 // But if it's within finite range, then either it's 1) an exact value and so 29 // representable, or 2) it's "between two adjacent destination values" and 30 // safe to cast to "an implementation-defined choice of either of those 31 // values". 32 auto valueAsFloat = static_cast<float>(aValue); 33 34 // Per [conv.fpprom] this never changes value. 35 auto valueAsFloatAsDouble = static_cast<double>(valueAsFloat); 36 37 // Finally, in 1) exact representable value equals exact representable value, 38 // or 2) *changed* value does not equal original value, ergo unrepresentable. 39 return valueAsFloatAsDouble == aValue; 40 } 41 42 } /* namespace mozilla */