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/* -*- Mode: C++; tab-width: 2; 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
#ifndef ModuloBuffer_h
#define ModuloBuffer_h
#include "mozilla/leb128iterator.h"
#include "mozilla/Maybe.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/NotNull.h"
#include "mozilla/PowerOfTwo.h"
#include "mozilla/ProfileBufferEntrySerialization.h"
#include "mozilla/UniquePtr.h"
#include <functional>
#include <iterator>
#include <limits>
#include <type_traits>
namespace mozilla {
// The ModuloBuffer class is a circular buffer that holds raw byte values, with
// data-read/write helpers.
//
// OffsetT: Type of the internal offset into the buffer of bytes, it should be
// large enough to access all bytes of the buffer. It will also be used as
// Length (in bytes) of the buffer and of any subset. Default uint32_t
// IndexT: Type of the external index, it should be large enough that overflows
// should not happen during the lifetime of the ModuloBuffer.
//
// The basic usage is to create an iterator-like object with `ReaderAt(Index)`
// or `WriterAt(Index)`, and use it to read/write data blobs. Iterators
// automatically manage the wrap-around (through "Modulo", which is effectively
// an AND-masking with the PowerOfTwo buffer size.)
//
// There is zero safety: No thread safety, no checks that iterators may be
// overwriting data that's still to be read, etc. It's up to the caller to add
// adequate checks.
// The intended use is as an underlying buffer for a safer container.
template <typename OffsetT = uint32_t, typename IndexT = uint64_t>
class ModuloBuffer {
public:
using Byte = uint8_t;
static_assert(sizeof(Byte) == 1, "ModuloBuffer::Byte must be 1 byte");
using Offset = OffsetT;
static_assert(!std::numeric_limits<Offset>::is_signed,
"ModuloBuffer::Offset must be an unsigned integral type");
using Length = Offset;
using Index = IndexT;
static_assert(!std::numeric_limits<Index>::is_signed,
"ModuloBuffer::Index must be an unsigned integral type");
static_assert(sizeof(Index) >= sizeof(Offset),
"ModuloBuffer::Index size must >= Offset");
// Create a buffer of the given length.
explicit ModuloBuffer(PowerOfTwo<Length> aLength)
: mMask(aLength.Mask()),
mBuffer(WrapNotNull(new Byte[aLength.Value()])),
mBufferDeleter([](Byte* aBuffer) { delete[] aBuffer; }) {}
// Take ownership of an existing buffer. Existing contents is ignored.
// Done by extracting the raw pointer from UniquePtr<Byte[]>, and adding
// an equivalent `delete[]` in `mBufferDeleter`.
ModuloBuffer(UniquePtr<Byte[]> aExistingBuffer, PowerOfTwo<Length> aLength)
: mMask(aLength.Mask()),
mBuffer(WrapNotNull(aExistingBuffer.release())),
mBufferDeleter([](Byte* aBuffer) { delete[] aBuffer; }) {}
// Use an externally-owned buffer. Existing contents is ignored.
ModuloBuffer(Byte* aExternalBuffer, PowerOfTwo<Length> aLength)
: mMask(aLength.Mask()), mBuffer(WrapNotNull(aExternalBuffer)) {}
// Disallow copying, as we may uniquely own the resource.
ModuloBuffer(const ModuloBuffer& aOther) = delete;
ModuloBuffer& operator=(const ModuloBuffer& aOther) = delete;
// Allow move-construction. Stealing ownership if the original had it.
// This effectively prevents copy construction, and all assignments; needed so
// that a ModuloBuffer may be initialized from a separate construction.
// The moved-from ModuloBuffer still points at the resource but doesn't own
// it, so it won't try to free it; but accesses are not guaranteed, so it
// should not be used anymore.
ModuloBuffer(ModuloBuffer&& aOther)
: mMask(std::move(aOther.mMask)),
mBuffer(std::move(aOther.mBuffer)),
mBufferDeleter(std::move(aOther.mBufferDeleter)) {
// The above move leaves `aOther.mBufferDeleter` in a valid state but with
// an unspecified value, so it could theoretically still contain the
// original function, which would be bad because we don't want aOther to
// delete the resource that `this` now owns.
if (aOther.mBufferDeleter) {
// `aOther` still had a non-empty deleter, reset it.
aOther.mBufferDeleter = nullptr;
}
}
// Disallow assignment, as we have some `const` members.
ModuloBuffer& operator=(ModuloBuffer&& aOther) = delete;
// Destructor, deletes the resource if we uniquely own it.
~ModuloBuffer() {
if (mBufferDeleter) {
mBufferDeleter(mBuffer);
}
}
PowerOfTwo<Length> BufferLength() const {
return PowerOfTwo<Length>(mMask.MaskValue() + 1);
}
// Size of external resources.
// Note: `mBufferDeleter`'s potential external data (for its captures) is not
// included, as it's hidden in the `std::function` implementation.
size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const {
if (!mBufferDeleter) {
// If we don't have a buffer deleter, assume we don't own the data, so
// it's probably on the stack, or should be reported by its owner.
return 0;
}
return aMallocSizeOf(mBuffer);
}
size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const {
return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
}
ProfileBufferEntryReader EntryReaderFromTo(
Index aStart, Index aEnd, ProfileBufferBlockIndex aBlockIndex,
ProfileBufferBlockIndex aNextBlockIndex) const {
using EntrySpan = Span<const ProfileBufferEntryReader::Byte>;
if (aStart == aEnd) {
return ProfileBufferEntryReader{};
}
// Don't allow over-wrapping.
MOZ_ASSERT(aEnd - aStart <= mMask.MaskValue() + 1);
// Start offset in 0 .. (buffer size - 1)
Offset start = static_cast<Offset>(aStart) & mMask;
// End offset in 1 .. (buffer size)
Offset end = (static_cast<Offset>(aEnd - 1) & mMask) + 1;
if (start < end) {
// Segment doesn't cross buffer threshold, one span is enough.
return ProfileBufferEntryReader{EntrySpan(&mBuffer[start], end - start),
aBlockIndex, aNextBlockIndex};
}
// Segment crosses buffer threshold, we need one span until the end and one
// span restarting at the beginning of the buffer.
return ProfileBufferEntryReader{
EntrySpan(&mBuffer[start], mMask.MaskValue() + 1 - start),
EntrySpan(&mBuffer[0], end), aBlockIndex, aNextBlockIndex};
}
// Return an entry writer for the given range.
ProfileBufferEntryWriter EntryWriterFromTo(Index aStart, Index aEnd) const {
using EntrySpan = Span<ProfileBufferEntryReader::Byte>;
if (aStart == aEnd) {
return ProfileBufferEntryWriter{};
}
MOZ_ASSERT(aEnd - aStart <= mMask.MaskValue() + 1);
// Start offset in 0 .. (buffer size - 1)
Offset start = static_cast<Offset>(aStart) & mMask;
// End offset in 1 .. (buffer size)
Offset end = (static_cast<Offset>(aEnd - 1) & mMask) + 1;
if (start < end) {
// Segment doesn't cross buffer threshold, one span is enough.
return ProfileBufferEntryWriter{
EntrySpan(&mBuffer[start], end - start),
ProfileBufferBlockIndex::CreateFromProfileBufferIndex(aStart),
ProfileBufferBlockIndex::CreateFromProfileBufferIndex(aEnd)};
}
// Segment crosses buffer threshold, we need one span until the end and one
// span restarting at the beginning of the buffer.
return ProfileBufferEntryWriter{
EntrySpan(&mBuffer[start], mMask.MaskValue() + 1 - start),
EntrySpan(&mBuffer[0], end),
ProfileBufferBlockIndex::CreateFromProfileBufferIndex(aStart),
ProfileBufferBlockIndex::CreateFromProfileBufferIndex(aEnd)};
}
// Emplace an entry writer into `aMaybeEntryWriter` for the given range.
void EntryWriterFromTo(Maybe<ProfileBufferEntryWriter>& aMaybeEntryWriter,
Index aStart, Index aEnd) const {
MOZ_ASSERT(aMaybeEntryWriter.isNothing(),
"Reference entry writer should be Nothing.");
using EntrySpan = Span<ProfileBufferEntryReader::Byte>;
if (aStart == aEnd) {
return;
}
MOZ_ASSERT(aEnd - aStart <= mMask.MaskValue() + 1);
// Start offset in 0 .. (buffer size - 1)
Offset start = static_cast<Offset>(aStart) & mMask;
// End offset in 1 .. (buffer size)
Offset end = (static_cast<Offset>(aEnd - 1) & mMask) + 1;
if (start < end) {
// Segment doesn't cross buffer threshold, one span is enough.
aMaybeEntryWriter.emplace(
EntrySpan(&mBuffer[start], end - start),
ProfileBufferBlockIndex::CreateFromProfileBufferIndex(aStart),
ProfileBufferBlockIndex::CreateFromProfileBufferIndex(aEnd));
} else {
// Segment crosses buffer threshold, we need one span until the end and
// one span restarting at the beginning of the buffer.
aMaybeEntryWriter.emplace(
EntrySpan(&mBuffer[start], mMask.MaskValue() + 1 - start),
EntrySpan(&mBuffer[0], end),
ProfileBufferBlockIndex::CreateFromProfileBufferIndex(aStart),
ProfileBufferBlockIndex::CreateFromProfileBufferIndex(aEnd));
}
}
// All ModuloBuffer operations should be done through this iterator, which has
// an effectively infinite range. The underlying wrapping-around is hidden.
// Use `ReaderAt(Index)` or `WriterAt(Index)` to create it.
//
// `const Iterator<...>` means the iterator itself cannot change, i.e., it
// cannot move, and only its const methods are available. Note that these
// const methods may still be used to modify the buffer contents (e.g.:
// `operator*()`, `Poke()`).
//
// `Iterator</*IsBufferConst=*/true>` means the buffer contents cannot be
// modified, i.e., write operations are forbidden, but the iterator may still
// move if non-const itself.
template <bool IsBufferConst>
class Iterator {
// Alias to const- or mutable-`ModuloBuffer` depending on `IsBufferConst`.
using ConstOrMutableBuffer =
std::conditional_t<IsBufferConst, const ModuloBuffer, ModuloBuffer>;
// Implementation note about the strange enable-if's below:
// `template <bool NotIBC = !IsBufferConst> enable_if_t<NotIBC>`
// which intuitively could be simplified to:
// `enable_if_t<!IsBufferConst>`
// The former extra-templated syntax is in fact necessary to delay
// instantiation of these functions until they are actually needed.
//
// If we were just doing `enable_if_t<!IsBufferConst>`, this would only
// depend on the *class* (`ModuloBuffer<...>::Iterator`), which gets
// instantiated when a `ModuloBuffer` is created with some template
// arguments; at that point, all non-templated methods get instantiated, so
// there's no "SFINAE" happening, and `enable_if_t<...>` is actually doing
// `typename enable_if<...>::type` on the spot, but there is no `type` if
// `IsBufferConst` is true, so it just fails right away. E.g.:
// error: no type named 'type' in 'std::enable_if<false, void>';
// 'enable_if' cannot be used to disable this declaration
// note: in instantiation of template type alias 'enable_if_t'
// > std::enable_if_t<!IsBufferConst> WriteObject(const T& aObject) {
// in instantiation of template class
// 'mozilla::ModuloBuffer<...>::Iterator<true>'
// > auto it = mb.ReaderAt(1);
//
// By adding another template level `template <bool NotIsBufferConst =
// !IsBufferConst>`, the instantiation is delayed until the function is
// actually invoked somewhere, e.g. `it.Poke(...);`.
// So at that invocation point, the compiler looks for a "Poke" name in it,
// and considers potential template instantiations that could work. The
// `enable_if_t` is *now* attempted, with `NotIsBufferConst` taking its
// value from `!IsBufferConst`:
// - If `IsBufferConst` is false, `NotIsBufferConst` is true,
// `enable_if<NotIsBufferConst>` does define a `type` (`void` by default),
// so `enable_if_t` happily becomes `void`, the function exists and may be
// called.
// - Otherwise if `IsBufferConst` is true, `NotIsBufferConst` is false,
// `enable_if<NotIsBufferConst>` does *not* define a `type`, therefore
// `enable_if_t` produces an error because there is no `type`. Now "SFINAE"
// happens: This "Substitution Failure Is Not An Error" (by itself)... But
// then, there are no other functions named "Poke" as requested in the
// `it.Poke(...);` call, so we are now getting an error (can't find
// function), as expected because `it` had `IsBufferConst`==true. (But at
// least the compiler waited until this invocation attempt before outputting
// an error.)
//
// C++ is fun!
public:
// These definitions are expected by std functions, to recognize this as an
using difference_type = Index;
using value_type = Byte;
using pointer = std::conditional_t<IsBufferConst, const Byte*, Byte*>;
using reference = std::conditional_t<IsBufferConst, const Byte&, Byte&>;
using iterator_category = std::random_access_iterator_tag;
// Can always copy/assign from the same kind of iterator.
Iterator(const Iterator& aRhs) = default;
Iterator& operator=(const Iterator& aRhs) = default;
// Can implicitly copy an Iterator-to-mutable (reader+writer) to
// Iterator-to-const (reader-only), but not the reverse.
template <bool IsRhsBufferConst,
typename = std::enable_if_t<(!IsRhsBufferConst) && IsBufferConst>>
MOZ_IMPLICIT Iterator(const Iterator<IsRhsBufferConst>& aRhs)
: mModuloBuffer(aRhs.mModuloBuffer), mIndex(aRhs.mIndex) {}
// Can implicitly assign from an Iterator-to-mutable (reader+writer) to
// Iterator-to-const (reader-only), but not the reverse.
template <bool IsRhsBufferConst,
typename = std::enable_if_t<(!IsRhsBufferConst) && IsBufferConst>>
Iterator& operator=(const Iterator<IsRhsBufferConst>& aRhs) {
mModuloBuffer = aRhs.mModuloBuffer;
mIndex = aRhs.mIndex;
return *this;
}
// Current location of the iterator in the `Index` range.
// Note that due to wrapping, multiple indices may effectively point at the
// same byte in the buffer.
Index CurrentIndex() const { return mIndex; }
// Location comparison in the `Index` range. I.e., two `Iterator`s may look
// unequal, but refer to the same buffer location.
// Must be on the same buffer.
bool operator==(const Iterator& aRhs) const {
MOZ_ASSERT(mModuloBuffer == aRhs.mModuloBuffer);
return mIndex == aRhs.mIndex;
}
bool operator!=(const Iterator& aRhs) const {
MOZ_ASSERT(mModuloBuffer == aRhs.mModuloBuffer);
return mIndex != aRhs.mIndex;
}
bool operator<(const Iterator& aRhs) const {
MOZ_ASSERT(mModuloBuffer == aRhs.mModuloBuffer);
return mIndex < aRhs.mIndex;
}
bool operator<=(const Iterator& aRhs) const {
MOZ_ASSERT(mModuloBuffer == aRhs.mModuloBuffer);
return mIndex <= aRhs.mIndex;
}
bool operator>(const Iterator& aRhs) const {
MOZ_ASSERT(mModuloBuffer == aRhs.mModuloBuffer);
return mIndex > aRhs.mIndex;
}
bool operator>=(const Iterator& aRhs) const {
MOZ_ASSERT(mModuloBuffer == aRhs.mModuloBuffer);
return mIndex >= aRhs.mIndex;
}
// Movement in the `Index` range.
Iterator& operator++() {
++mIndex;
return *this;
}
Iterator operator++(int) {
Iterator here(*mModuloBuffer, mIndex);
++mIndex;
return here;
}
Iterator& operator--() {
--mIndex;
return *this;
}
Iterator operator--(int) {
Iterator here(*mModuloBuffer, mIndex);
--mIndex;
return here;
}
Iterator& operator+=(Length aLength) {
mIndex += aLength;
return *this;
}
Iterator operator+(Length aLength) const {
return Iterator(*mModuloBuffer, mIndex + aLength);
}
friend Iterator operator+(Length aLength, const Iterator& aIt) {
return aIt + aLength;
}
Iterator& operator-=(Length aLength) {
mIndex -= aLength;
return *this;
}
Iterator operator-(Length aLength) const {
return Iterator(*mModuloBuffer, mIndex - aLength);
}
// Distance from `aRef` to here in the `Index` range.
// May be negative (as 2's complement) if `aRef > *this`.
Index operator-(const Iterator& aRef) const {
MOZ_ASSERT(mModuloBuffer == aRef.mModuloBuffer);
return mIndex - aRef.mIndex;
}
// Dereference a single byte (read-only if `IsBufferConst` is true).
reference operator*() const {
return mModuloBuffer->mBuffer[OffsetInBuffer()];
}
// Random-access dereference.
reference operator[](Length aLength) const { return *(*this + aLength); }
// Write data (if `IsBufferConst` is false) but don't move iterator.
template <bool NotIsBufferConst = !IsBufferConst>
std::enable_if_t<NotIsBufferConst> Poke(const void* aSrc,
Length aLength) const {
// Don't allow data larger than the buffer.
MOZ_ASSERT(aLength <= mModuloBuffer->BufferLength().Value());
// Offset inside the buffer (corresponding to our Index).
Offset offset = OffsetInBuffer();
// Compute remaining bytes between this offset and the end of the buffer.
Length remaining = mModuloBuffer->BufferLength().Value() - offset;
if (MOZ_LIKELY(remaining >= aLength)) {
// Enough space to write everything before the end.
memcpy(&mModuloBuffer->mBuffer[offset], aSrc, aLength);
} else {
// Not enough space. Write as much as possible before the end.
memcpy(&mModuloBuffer->mBuffer[offset], aSrc, remaining);
// And then continue from the beginning of the buffer.
memcpy(&mModuloBuffer->mBuffer[0],
static_cast<const Byte*>(aSrc) + remaining,
(aLength - remaining));
}
}
// Write object data (if `IsBufferConst` is false) but don't move iterator.
// Note that this copies bytes from the object, with the intent to read them
// back later. Restricted to trivially-copyable types, which support this
// without Undefined Behavior!
template <typename T, bool NotIsBufferConst = !IsBufferConst>
std::enable_if_t<NotIsBufferConst> PokeObject(const T& aObject) const {
static_assert(std::is_trivially_copyable<T>::value,
"PokeObject<T> - T must be trivially copyable");
return Poke(&aObject, sizeof(T));
}
// Write data (if `IsBufferConst` is false) and move iterator ahead.
template <bool NotIsBufferConst = !IsBufferConst>
std::enable_if_t<NotIsBufferConst> Write(const void* aSrc, Length aLength) {
Poke(aSrc, aLength);
mIndex += aLength;
}
// Write object data (if `IsBufferConst` is false) and move iterator ahead.
// Note that this copies bytes from the object, with the intent to read them
// back later. Restricted to trivially-copyable types, which support this
// without Undefined Behavior!
template <typename T, bool NotIsBufferConst = !IsBufferConst>
std::enable_if_t<NotIsBufferConst> WriteObject(const T& aObject) {
static_assert(std::is_trivially_copyable<T>::value,
"WriteObject<T> - T must be trivially copyable");
return Write(&aObject, sizeof(T));
}
// Number of bytes needed to represent `aValue` in unsigned LEB128.
template <typename T>
static unsigned ULEB128Size(T aValue) {
return ::mozilla::ULEB128Size(aValue);
}
// Write number as unsigned LEB128 (if `IsBufferConst` is false) and move
// iterator ahead.
template <typename T, bool NotIsBufferConst = !IsBufferConst>
std::enable_if_t<NotIsBufferConst> WriteULEB128(T aValue) {
::mozilla::WriteULEB128(aValue, *this);
}
// Read data but don't move iterator.
void Peek(void* aDst, Length aLength) const {
// Don't allow data larger than the buffer.
MOZ_ASSERT(aLength <= mModuloBuffer->BufferLength().Value());
// Offset inside the buffer (corresponding to our Index).
Offset offset = OffsetInBuffer();
// Compute remaining bytes between this offset and the end of the buffer.
Length remaining = mModuloBuffer->BufferLength().Value() - offset;
if (MOZ_LIKELY(remaining >= aLength)) {
// Can read everything we need before the end of the buffer.
memcpy(aDst, &mModuloBuffer->mBuffer[offset], aLength);
} else {
// Read as much as possible before the end of the buffer.
memcpy(aDst, &mModuloBuffer->mBuffer[offset], remaining);
// And then continue from the beginning of the buffer.
memcpy(static_cast<Byte*>(aDst) + remaining, &mModuloBuffer->mBuffer[0],
(aLength - remaining));
}
}
// Read data into an object but don't move iterator.
// Note that this overwrites `aObject` with bytes from the buffer.
// Restricted to trivially-copyable types, which support this without
// Undefined Behavior!
template <typename T>
void PeekIntoObject(T& aObject) const {
static_assert(std::is_trivially_copyable<T>::value,
"PeekIntoObject<T> - T must be trivially copyable");
Peek(&aObject, sizeof(T));
}
// Read data as an object but don't move iterator.
// Note that this creates an default `T` first, and then overwrites it with
// bytes from the buffer. Restricted to trivially-copyable types, which
// support this without Undefined Behavior!
template <typename T>
T PeekObject() const {
static_assert(std::is_trivially_copyable<T>::value,
"PeekObject<T> - T must be trivially copyable");
T object;
PeekIntoObject(object);
return object;
}
// Read data and move iterator ahead.
void Read(void* aDst, Length aLength) {
Peek(aDst, aLength);
mIndex += aLength;
}
// Read data into a mutable iterator and move both iterators ahead.
void ReadInto(Iterator</* IsBufferConst */ false>& aDst, Length aLength) {
// Don't allow data larger than the buffer.
MOZ_ASSERT(aLength <= mModuloBuffer->BufferLength().Value());
MOZ_ASSERT(aLength <= aDst.mModuloBuffer->BufferLength().Value());
// Offset inside the buffer (corresponding to our Index).
Offset offset = OffsetInBuffer();
// Compute remaining bytes between this offset and the end of the buffer.
Length remaining = mModuloBuffer->BufferLength().Value() - offset;
if (MOZ_LIKELY(remaining >= aLength)) {
// Can read everything we need before the end of the buffer.
aDst.Write(&mModuloBuffer->mBuffer[offset], aLength);
} else {
// Read as much as possible before the end of the buffer.
aDst.Write(&mModuloBuffer->mBuffer[offset], remaining);
// And then continue from the beginning of the buffer.
aDst.Write(&mModuloBuffer->mBuffer[0], (aLength - remaining));
}
mIndex += aLength;
}
// Read data into an object and move iterator ahead.
// Note that this overwrites `aObject` with bytes from the buffer.
// Restricted to trivially-copyable types, which support this without
// Undefined Behavior!
template <typename T>
void ReadIntoObject(T& aObject) {
static_assert(std::is_trivially_copyable<T>::value,
"ReadIntoObject<T> - T must be trivially copyable");
Read(&aObject, sizeof(T));
}
// Read data as an object and move iterator ahead.
// Note that this creates an default `T` first, and then overwrites it with
// bytes from the buffer. Restricted to trivially-copyable types, which
// support this without Undefined Behavior!
template <typename T>
T ReadObject() {
static_assert(std::is_trivially_copyable<T>::value,
"ReadObject<T> - T must be trivially copyable");
T object;
ReadIntoObject(object);
return object;
}
// Read an unsigned LEB128 number and move iterator ahead.
template <typename T>
T ReadULEB128() {
return ::mozilla::ReadULEB128<T>(*this);
}
private:
// Only a ModuloBuffer can instantiate its iterator.
friend class ModuloBuffer;
Iterator(ConstOrMutableBuffer& aBuffer, Index aIndex)
: mModuloBuffer(WrapNotNull(&aBuffer)), mIndex(aIndex) {}
// Convert the Iterator's mIndex into an offset inside the byte buffer.
Offset OffsetInBuffer() const {
return static_cast<Offset>(mIndex) & mModuloBuffer->mMask;
}
// ModuloBuffer that this Iterator operates on.
// Using a non-null pointer instead of a reference, to allow re-assignment
// of an Iterator variable.
NotNull<ConstOrMutableBuffer*> mModuloBuffer;
// Position of this iterator in the wider `Index` range. (Will be wrapped
// around as needed when actually accessing bytes from the buffer.)
Index mIndex;
};
// Shortcut to iterator to const (read-only) data.
using Reader = Iterator<true>;
// Shortcut to iterator to non-const (read/write) data.
using Writer = Iterator<false>;
// Create an iterator to const data at the given index.
Reader ReaderAt(Index aIndex) const { return Reader(*this, aIndex); }
// Create an iterator to non-const data at the given index.
Writer WriterAt(Index aIndex) { return Writer(*this, aIndex); }
#ifdef DEBUG
void Dump() const {
Length len = BufferLength().Value();
if (len > 128) {
len = 128;
}
for (Length i = 0; i < len; ++i) {
printf("%02x ", mBuffer[i]);
}
printf("\n");
}
#endif // DEBUG
private:
// Mask used to convert an index to an offset in `mBuffer`
const PowerOfTwoMask<Offset> mMask;
// Buffer data. `const NotNull<...>` shows that `mBuffer is `const`, and
// `Byte* const` shows that the pointer cannot be changed to point at
// something else, but the pointed-at `Byte`s are writable.
const NotNull<Byte* const> mBuffer;
// Function used to release the buffer resource (if needed).
std::function<void(Byte*)> mBufferDeleter;
};
} // namespace mozilla
#endif // ModuloBuffer_h