| // 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__ |