blob: 6aca16720f923d1f4dc157f24795f82b7a4e9d33 [file] [log] [blame]
// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
// This file provides alignment utilities for use in arenas.
//
// `ArenaAlign` contains a single `align` data member and provides
// the below functions which operate on the given alignment.
//
// Ceil(size_t n) - rounds `n` up to the nearest `align` boundary.
// Floor(size_t n) - rounds `n` down to the nearest `align` boundary.
// Padded(size_t n) - returns the unaligned size to align 'n' bytes. (1)
// Ceil(T* P) - rounds `p` up to the nearest `align` boundary. (2)
// IsAligned(size_t n) - returns true if `n` is aligned to `align`
// IsAligned(T* p) - returns true if `p` is aligned to `align`
// CheckAligned(T* p) - returns `p`. Checks alignment of `p` in debug.
//
// 1) `Padded(n)` returns the minimum size needed to align an object of size 'n'
// into a memory area that is default aligned. For example, allocating 'n'
// bytes aligned at 32 bytes requires a size of 'n + 32 - 8' to align at 32
// bytes for any 8 byte boundary.
//
// 2) There is an optimized `CeilDefaultAligned(T*)` method which is equivalent
// to `Ceil(ArenaAlignDefault::CheckAlign(p))` but more efficiently
// implemented as a 'check only' for ArenaAlignDefault.
//
// These classes allow for generic arena logic using 'alignment policies'.
//
// For example:
//
// template <Align>
// void* NaiveAlloc(size_t n, Align align) {
// ABSL_ASSERT(align.IsAligned(n));
// const size_t required = align.Padded(n);
// if (required <= static_cast<size_t>(ptr_ - limit_)) {
// uint8_t* ptr = align.CeilDefaultAligned(ptr_);
// ptr_ = ptr + n;
// return ptr;
// }
// return nullptr;
// }
//
// void CallSites() {
// void *p1 = NaiveAlloc(n, ArenaAlignDefault());
// void *p2 = NaiveAlloc(n, ArenaAlignAs(32));
// }
//
#ifndef GOOGLE_PROTOBUF_ARENA_ALIGN_H__
#define GOOGLE_PROTOBUF_ARENA_ALIGN_H__
#include <cstddef>
#include <cstdint>
#include "absl/base/macros.h"
#include "absl/log/absl_check.h"
#include "absl/numeric/bits.h"
// Must be included last.
#include "google/protobuf/port_def.inc"
namespace google {
namespace protobuf {
namespace internal {
struct ArenaAlignDefault {
PROTOBUF_EXPORT static constexpr size_t align = 8; // NOLINT
static constexpr bool IsAligned(size_t n) { return (n & (align - 1)) == 0U; }
template <typename T>
static PROTOBUF_ALWAYS_INLINE bool IsAligned(T* ptr) {
return (reinterpret_cast<uintptr_t>(ptr) & (align - 1)) == 0U;
}
static PROTOBUF_ALWAYS_INLINE constexpr size_t Ceil(size_t n) {
return (n + align - 1) & ~(align - 1);
}
static PROTOBUF_ALWAYS_INLINE constexpr size_t Floor(size_t n) {
return (n & ~(align - 1));
}
static PROTOBUF_ALWAYS_INLINE size_t Padded(size_t n) {
ABSL_ASSERT(IsAligned(n));
return n;
}
template <typename T>
static PROTOBUF_ALWAYS_INLINE T* Ceil(T* ptr) {
uintptr_t intptr = reinterpret_cast<uintptr_t>(ptr);
return reinterpret_cast<T*>((intptr + align - 1) & ~(align - 1));
}
template <typename T>
static PROTOBUF_ALWAYS_INLINE T* CeilDefaultAligned(T* ptr) {
ABSL_ASSERT(IsAligned(ptr));
return ptr;
}
// Address sanitizer enabled alignment check
template <typename T>
static PROTOBUF_ALWAYS_INLINE T* CheckAligned(T* ptr) {
ABSL_ASSERT(IsAligned(ptr));
return ptr;
}
};
struct ArenaAlign {
static constexpr bool IsDefault() { return false; };
size_t align;
constexpr bool IsAligned(size_t n) const { return (n & (align - 1)) == 0U; }
template <typename T>
bool IsAligned(T* ptr) const {
return (reinterpret_cast<uintptr_t>(ptr) & (align - 1)) == 0U;
}
constexpr size_t Ceil(size_t n) const {
return (n + align - 1) & ~(align - 1);
}
constexpr size_t Floor(size_t n) const { return (n & ~(align - 1)); }
constexpr size_t Padded(size_t n) const {
// TODO: there are direct callers of AllocateAligned() that violate
// `size` being a multiple of `align`: that should be an error / assert.
// ABSL_ASSERT(IsAligned(n));
ABSL_ASSERT(ArenaAlignDefault::IsAligned(align));
return n + align - ArenaAlignDefault::align;
}
template <typename T>
T* Ceil(T* ptr) const {
uintptr_t intptr = reinterpret_cast<uintptr_t>(ptr);
return reinterpret_cast<T*>((intptr + align - 1) & ~(align - 1));
}
template <typename T>
T* CeilDefaultAligned(T* ptr) const {
ABSL_ASSERT(ArenaAlignDefault::IsAligned(ptr));
return Ceil(ptr);
}
// Address sanitizer enabled alignment check
template <typename T>
T* CheckAligned(T* ptr) const {
ABSL_ASSERT(IsAligned(ptr));
return ptr;
}
};
inline ArenaAlign ArenaAlignAs(size_t align) {
// align must be a non zero power of 2 >= 8
ABSL_DCHECK_NE(align, 0U);
ABSL_DCHECK(absl::has_single_bit(align)) << "Invalid alignment " << align;
return ArenaAlign{align};
}
template <bool, size_t align>
struct AlignFactory {
static_assert(align > ArenaAlignDefault::align, "Not over-aligned");
static_assert((align & (align - 1)) == 0U, "Not power of 2");
static constexpr ArenaAlign Create() { return ArenaAlign{align}; }
};
template <size_t align>
struct AlignFactory<true, align> {
static_assert(align <= ArenaAlignDefault::align, "Over-aligned");
static_assert((align & (align - 1)) == 0U, "Not power of 2");
static constexpr ArenaAlignDefault Create() { return ArenaAlignDefault{}; }
};
// Returns an `ArenaAlignDefault` instance for `align` less than or equal to the
// default alignment, and `AlignAs(align)` for over-aligned values of `align`.
// The purpose is to take advantage of invoking functions accepting a template
// overloaded 'Align align` argument reducing the alignment operations on
// `ArenaAlignDefault` implementations to no-ops.
template <size_t align>
inline constexpr auto ArenaAlignAs() {
return AlignFactory<align <= ArenaAlignDefault::align, align>::Create();
}
// Returns ArenaAlignAs<alignof(T)>
template <typename T>
inline constexpr auto ArenaAlignOf() {
return ArenaAlignAs<alignof(T)>();
}
} // namespace internal
} // namespace protobuf
} // namespace google
#include "google/protobuf/port_undef.inc"
#endif // GOOGLE_PROTOBUF_ARENA_ALIGN_H__