memory.h 2.52 KB
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// Copyright 2011 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
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#ifndef V8_BASE_MEMORY_H_
#define V8_BASE_MEMORY_H_
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#include "src/base/macros.h"
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#include "src/base/platform/wrappers.h"
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namespace v8 {
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namespace base {

using Address = uintptr_t;
using byte = uint8_t;
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// Memory provides an interface to 'raw' memory. It encapsulates the casts
// that typically are needed when incompatible pointer types are used.
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// Note that this class currently relies on undefined behaviour. There is a
// proposal (http://wg21.link/p0593r2) to make it defined behaviour though.
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template <class T>
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inline T& Memory(Address addr) {
  DCHECK(IsAligned(addr, alignof(T)));
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  return *reinterpret_cast<T*>(addr);
}
template <class T>
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inline T& Memory(byte* addr) {
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  return Memory<T>(reinterpret_cast<Address>(addr));
}
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template <typename V>
static inline V ReadUnalignedValue(Address p) {
  ASSERT_TRIVIALLY_COPYABLE(V);
  V r;
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  base::Memcpy(&r, reinterpret_cast<void*>(p), sizeof(V));
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  return r;
}

template <typename V>
static inline void WriteUnalignedValue(Address p, V value) {
  ASSERT_TRIVIALLY_COPYABLE(V);
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  base::Memcpy(reinterpret_cast<void*>(p), &value, sizeof(V));
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}

template <typename V>
static inline V ReadLittleEndianValue(Address p) {
#if defined(V8_TARGET_LITTLE_ENDIAN)
  return ReadUnalignedValue<V>(p);
#elif defined(V8_TARGET_BIG_ENDIAN)
  V ret{};
  const byte* src = reinterpret_cast<const byte*>(p);
  byte* dst = reinterpret_cast<byte*>(&ret);
  for (size_t i = 0; i < sizeof(V); i++) {
    dst[i] = src[sizeof(V) - i - 1];
  }
  return ret;
#endif  // V8_TARGET_LITTLE_ENDIAN
}

template <typename V>
static inline void WriteLittleEndianValue(Address p, V value) {
#if defined(V8_TARGET_LITTLE_ENDIAN)
  WriteUnalignedValue<V>(p, value);
#elif defined(V8_TARGET_BIG_ENDIAN)
  byte* src = reinterpret_cast<byte*>(&value);
  byte* dst = reinterpret_cast<byte*>(p);
  for (size_t i = 0; i < sizeof(V); i++) {
    dst[i] = src[sizeof(V) - i - 1];
  }
#endif  // V8_TARGET_LITTLE_ENDIAN
}

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template <typename V>
static inline V ReadLittleEndianValue(V* p) {
  return ReadLittleEndianValue<V>(reinterpret_cast<Address>(p));
}

template <typename V>
static inline void WriteLittleEndianValue(V* p, V value) {
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  static_assert(
      !std::is_array<V>::value,
      "Passing an array decays to pointer, causing unexpected results.");
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  WriteLittleEndianValue<V>(reinterpret_cast<Address>(p), value);
}

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}  // namespace base
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}  // namespace v8
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#endif  // V8_BASE_MEMORY_H_