mfbt/FloatingPoint.cpp
author Petru Lingurar <petru.lingurar@softvision.ro>
Fri, 21 Dec 2018 08:56:47 +0000
changeset 501492 65621d0fe1262af0643cec37c23b2d9ec42588ad
parent 478641 b1521154cfec6b35f8266af53efb24ebac260173
child 508163 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1513938 - Enforce a Bundle size limit and drop `privateSession` if exceeds it. r=JanH, a=jcristau The `privateSession` key would normally allow persisting the Private Browsing session across OOMs in Activity's Bundle. We need to do that to avoid storing private, sensible data on disk like we do with the normal browsing session. In some cases `privateSession` would contain a lot of data which, along with other possible concurrent transactions could overflow Binder's buffer which has a limited fixed size, currently 1Mb. To avoid this, we will drop `privateSession` from the Bundle if the resulting size is greater than a _speculative_ size of 300KBs which would mean that in the case of an OOM all Private Browsing state would be lost. Bug 1515592 is filed to investigate for a better solution. Differential Revision: https://phabricator.services.mozilla.com/D15067

/* -*- 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 */