mfbt/TemplateLib.h
author Andrea Marchesini <amarchesini@mozilla.com>
Wed, 31 Oct 2018 18:30:18 +0100
changeset 500246 544498045a9cfe55968fa6500bffbc3181869fce
parent 389528 eb11f699091d1fa8ce5dc0ef671868feeb179778
child 505383 6f3709b3878117466168c40affa7bca0b60cf75b
permissions -rw-r--r--
Bug 1486698 - Update Fetch+Stream implementation to throw when the stream is disturbed or locked, r=bz In this patch, I went through any place in DOM fetch code, where there are ReadableStreams and update the locked, disturbed, readable checks. Because we expose streams more often, we need an extra care in the use of ErrorResult objects. JS streams can now throw exceptions and we need to handle them. This patch also fixes a bug in FileStreamReader::CloseAndRelease() which could be called in case mReader creation fails.

/* -*- 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/. */

/*
 * Reusable template meta-functions on types and compile-time values.  Meta-
 * functions are placed inside the 'tl' namespace to avoid conflict with non-
 * meta functions of the same name (e.g., mozilla::tl::FloorLog2 vs.
 * mozilla::FloorLog2).
 *
 * When constexpr support becomes universal, we should probably use that instead
 * of some of these templates, for simplicity.
 */

#ifndef mozilla_TemplateLib_h
#define mozilla_TemplateLib_h

#include <limits.h>
#include <stddef.h>

#include "mozilla/TypeTraits.h"

namespace mozilla {

namespace tl {

/** Compute min/max. */
template<size_t Size, size_t... Rest>
struct Min
{
  static constexpr size_t value =
    Size < Min<Rest...>::value
    ? Size
    : Min<Rest...>::value;
};

template<size_t Size>
struct Min<Size>
{
  static constexpr size_t value = Size;
};

template<size_t Size, size_t... Rest>
struct Max
{
  static constexpr size_t value =
    Size > Max<Rest...>::value
    ? Size
    : Max<Rest...>::value;
};

template<size_t Size>
struct Max<Size>
{
  static constexpr size_t value = Size;
};

/** Compute floor(log2(i)). */
template<size_t I>
struct FloorLog2
{
  static const size_t value = 1 + FloorLog2<I / 2>::value;
};
template<> struct FloorLog2<0> { /* Error */ };
template<> struct FloorLog2<1> { static const size_t value = 0; };

/** Compute ceiling(log2(i)). */
template<size_t I>
struct CeilingLog2
{
  static const size_t value = FloorLog2<2 * I - 1>::value;
};

/** Round up to the nearest power of 2. */
template<size_t I>
struct RoundUpPow2
{
  static const size_t value = size_t(1) << CeilingLog2<I>::value;
};
template<>
struct RoundUpPow2<0>
{
  static const size_t value = 1;
};

/** Compute the number of bits in the given unsigned type. */
template<typename T>
struct BitSize
{
  static const size_t value = sizeof(T) * CHAR_BIT;
};

/**
 * Produce an N-bit mask, where N <= BitSize<size_t>::value.  Handle the
 * language-undefined edge case when N = BitSize<size_t>::value.
 */
template<size_t N>
struct NBitMask
{
  // Assert the precondition.  On success this evaluates to 0.  Otherwise it
  // triggers divide-by-zero at compile time: a guaranteed compile error in
  // C++11, and usually one in C++98.  Add this value to |value| to assure
  // its computation.
  static const size_t checkPrecondition =
    0 / size_t(N < BitSize<size_t>::value);
  static const size_t value = (size_t(1) << N) - 1 + checkPrecondition;
};
template<>
struct NBitMask<BitSize<size_t>::value>
{
  static const size_t value = size_t(-1);
};

/**
 * For the unsigned integral type size_t, compute a mask M for N such that
 * for all X, !(X & M) implies X * N will not overflow (w.r.t size_t)
 */
template<size_t N>
struct MulOverflowMask
{
  static const size_t value =
    ~NBitMask<BitSize<size_t>::value - CeilingLog2<N>::value>::value;
};
template<> struct MulOverflowMask<0> { /* Error */ };
template<> struct MulOverflowMask<1> { static const size_t value = 0; };

/**
 * And<bool...> computes the logical 'and' of its argument booleans.
 *
 * Examples:
 *   mozilla::t1::And<true, true>::value is true.
 *   mozilla::t1::And<true, false>::value is false.
 *   mozilla::t1::And<>::value is true.
 */

template<bool...>
struct And;

template<>
struct And<> : public TrueType { };

template<bool C1, bool... Cn>
struct And<C1, Cn...>
  : public Conditional<C1, And<Cn...>, FalseType>::Type { };

} // namespace tl

} // namespace mozilla

#endif /* mozilla_TemplateLib_h */