third_party/abseil-cpp/absl/base/internal/unaligned_access.h - src - Git at Google

 //
 // Copyright 2017 The Abseil Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //

 #ifndef ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_
 #define ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_

 #include <string.h>
 #include <cstdint>

 #include "absl/base/attributes.h"

 // unaligned APIs

 // Portable handling of unaligned loads, stores, and copies.
 // On some platforms, like ARM, the copy functions can be more efficient
 // then a load and a store.
 //
 // It is possible to implement all of these these using constant-length memcpy
 // calls, which is portable and will usually be inlined into simple loads and
 // stores if the architecture supports it. However, such inlining usually
 // happens in a pass that's quite late in compilation, which means the resulting
 // loads and stores cannot participate in many other optimizations, leading to
 // overall worse code.

 // The unaligned API is C++ only.  The declarations use C++ features
 // (namespaces, inline) which are absent or incompatible in C.
 #if defined(__cplusplus)

 #if defined(ADDRESS_SANITIZER) || defined(THREAD_SANITIZER) ||\
     defined(MEMORY_SANITIZER)
 // Consider we have an unaligned load/store of 4 bytes from address 0x...05.
 // AddressSanitizer will treat it as a 3-byte access to the range 05:07 and
 // will miss a bug if 08 is the first unaddressable byte.
 // ThreadSanitizer will also treat this as a 3-byte access to 05:07 and will
 // miss a race between this access and some other accesses to 08.
 // MemorySanitizer will correctly propagate the shadow on unaligned stores
 // and correctly report bugs on unaligned loads, but it may not properly
 // update and report the origin of the uninitialized memory.
 // For all three tools, replacing an unaligned access with a tool-specific
 // callback solves the problem.

 // Make sure uint16_t/uint32_t/uint64_t are defined.
 #include <stdint.h>

 extern "C" {
 uint16_t __sanitizer_unaligned_load16(const void *p);
 uint32_t __sanitizer_unaligned_load32(const void *p);
 uint64_t __sanitizer_unaligned_load64(const void *p);
 void __sanitizer_unaligned_store16(void *p, uint16_t v);
 void __sanitizer_unaligned_store32(void *p, uint32_t v);
 void __sanitizer_unaligned_store64(void *p, uint64_t v);
 }  // extern "C"

 namespace absl {

 inline uint16_t UnalignedLoad16(const void *p) {
   return __sanitizer_unaligned_load16(p);
 }

 inline uint32_t UnalignedLoad32(const void *p) {
   return __sanitizer_unaligned_load32(p);
 }

 inline uint64_t UnalignedLoad64(const void *p) {
   return __sanitizer_unaligned_load64(p);
 }

 inline void UnalignedStore16(void *p, uint16_t v) {
   __sanitizer_unaligned_store16(p, v);
 }

 inline void UnalignedStore32(void *p, uint32_t v) {
   __sanitizer_unaligned_store32(p, v);
 }

 inline void UnalignedStore64(void *p, uint64_t v) {
   __sanitizer_unaligned_store64(p, v);
 }

 }  // namespace absl

 #define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) (absl::UnalignedLoad16(_p))
 #define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) (absl::UnalignedLoad32(_p))
 #define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))

 #define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
   (absl::UnalignedStore16(_p, _val))
 #define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
   (absl::UnalignedStore32(_p, _val))
 #define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
   (absl::UnalignedStore64(_p, _val))

 #elif defined(__x86_64__) || defined(_M_X64) || defined(__i386) || \
     defined(_M_IX86) || defined(__ppc__) || defined(__PPC__) ||    \
     defined(__ppc64__) || defined(__PPC64__)

 // x86 and x86-64 can perform unaligned loads/stores directly;
 // modern PowerPC hardware can also do unaligned integer loads and stores;
 // but note: the FPU still sends unaligned loads and stores to a trap handler!

 #define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
   (*reinterpret_cast<const uint16_t *>(_p))
 #define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
   (*reinterpret_cast<const uint32_t *>(_p))
 #define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
   (*reinterpret_cast<const uint64_t *>(_p))

 #define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
   (*reinterpret_cast<uint16_t *>(_p) = (_val))
 #define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
   (*reinterpret_cast<uint32_t *>(_p) = (_val))
 #define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
   (*reinterpret_cast<uint64_t *>(_p) = (_val))

 #elif defined(__arm__) && \
       !defined(__ARM_ARCH_5__) && \
       !defined(__ARM_ARCH_5T__) && \
       !defined(__ARM_ARCH_5TE__) && \
       !defined(__ARM_ARCH_5TEJ__) && \
       !defined(__ARM_ARCH_6__) && \
       !defined(__ARM_ARCH_6J__) && \
       !defined(__ARM_ARCH_6K__) && \
       !defined(__ARM_ARCH_6Z__) && \
       !defined(__ARM_ARCH_6ZK__) && \
       !defined(__ARM_ARCH_6T2__)


 // ARMv7 and newer support native unaligned accesses, but only of 16-bit
 // and 32-bit values (not 64-bit); older versions either raise a fatal signal,
 // do an unaligned read and rotate the words around a bit, or do the reads very
 // slowly (trip through kernel mode). There's no simple #define that says just
 // "ARMv7 or higher", so we have to filter away all ARMv5 and ARMv6
 // sub-architectures. Newer gcc (>= 4.6) set an __ARM_FEATURE_ALIGNED #define,
 // so in time, maybe we can move on to that.
 //
 // This is a mess, but there's not much we can do about it.
 //
 // To further complicate matters, only LDR instructions (single reads) are
 // allowed to be unaligned, not LDRD (two reads) or LDM (many reads). Unless we
 // explicitly tell the compiler that these accesses can be unaligned, it can and
 // will combine accesses. On armcc, the way to signal this is done by accessing
 // through the type (uint32_t __packed *), but GCC has no such attribute
 // (it ignores __attribute__((packed)) on individual variables). However,
 // we can tell it that a _struct_ is unaligned, which has the same effect,
 // so we do that.

 namespace absl {
 namespace internal {

 struct Unaligned16Struct {
   uint16_t value;
   uint8_t dummy;  // To make the size non-power-of-two.
 } ABSL_ATTRIBUTE_PACKED;

 struct Unaligned32Struct {
   uint32_t value;
   uint8_t dummy;  // To make the size non-power-of-two.
 } ABSL_ATTRIBUTE_PACKED;

 }  // namespace internal
 }  // namespace absl

 #define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
   ((reinterpret_cast<const ::absl::internal::Unaligned16Struct *>(_p))->value)
 #define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
   ((reinterpret_cast<const ::absl::internal::Unaligned32Struct *>(_p))->value)

 #define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val)                          \
   ((reinterpret_cast< ::absl::internal::Unaligned16Struct *>(_p))->value = \
        (_val))
 #define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val)                          \
   ((reinterpret_cast< ::absl::internal::Unaligned32Struct *>(_p))->value = \
        (_val))

 namespace absl {

 inline uint64_t UnalignedLoad64(const void *p) {
   uint64_t t;
   memcpy(&t, p, sizeof t);
   return t;
 }

 inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }

 }  // namespace absl

 #define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))
 #define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
   (absl::UnalignedStore64(_p, _val))

 #else

 // ABSL_INTERNAL_NEED_ALIGNED_LOADS is defined when the underlying platform
 // doesn't support unaligned access.
 #define ABSL_INTERNAL_NEED_ALIGNED_LOADS

 // These functions are provided for architectures that don't support
 // unaligned loads and stores.

 namespace absl {

 inline uint16_t UnalignedLoad16(const void *p) {
   uint16_t t;
   memcpy(&t, p, sizeof t);
   return t;
 }

 inline uint32_t UnalignedLoad32(const void *p) {
   uint32_t t;
   memcpy(&t, p, sizeof t);
   return t;
 }

 inline uint64_t UnalignedLoad64(const void *p) {
   uint64_t t;
   memcpy(&t, p, sizeof t);
   return t;
 }

 inline void UnalignedStore16(void *p, uint16_t v) { memcpy(p, &v, sizeof v); }

 inline void UnalignedStore32(void *p, uint32_t v) { memcpy(p, &v, sizeof v); }

 inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }

 }  // namespace absl

 #define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) (absl::UnalignedLoad16(_p))
 #define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) (absl::UnalignedLoad32(_p))
 #define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))

 #define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
   (absl::UnalignedStore16(_p, _val))
 #define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
   (absl::UnalignedStore32(_p, _val))
 #define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
   (absl::UnalignedStore64(_p, _val))

 #endif

 #endif  // defined(__cplusplus), end of unaligned API

 #endif  // ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_
	//
	// Copyright 2017 The Abseil Authors.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.
	//

	#ifndef ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_
	#define ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_

	#include <string.h>
	#include <cstdint>

	#include "absl/base/attributes.h"

	// unaligned APIs

	// Portable handling of unaligned loads, stores, and copies.
	// On some platforms, like ARM, the copy functions can be more efficient
	// then a load and a store.
	//
	// It is possible to implement all of these these using constant-length memcpy
	// calls, which is portable and will usually be inlined into simple loads and
	// stores if the architecture supports it. However, such inlining usually
	// happens in a pass that's quite late in compilation, which means the resulting
	// loads and stores cannot participate in many other optimizations, leading to
	// overall worse code.

	// The unaligned API is C++ only. The declarations use C++ features
	// (namespaces, inline) which are absent or incompatible in C.
	#if defined(__cplusplus)

	#if defined(ADDRESS_SANITIZER) \|\| defined(THREAD_SANITIZER) \|\|\
	defined(MEMORY_SANITIZER)
	// Consider we have an unaligned load/store of 4 bytes from address 0x...05.
	// AddressSanitizer will treat it as a 3-byte access to the range 05:07 and
	// will miss a bug if 08 is the first unaddressable byte.
	// ThreadSanitizer will also treat this as a 3-byte access to 05:07 and will
	// miss a race between this access and some other accesses to 08.
	// MemorySanitizer will correctly propagate the shadow on unaligned stores
	// and correctly report bugs on unaligned loads, but it may not properly
	// update and report the origin of the uninitialized memory.
	// For all three tools, replacing an unaligned access with a tool-specific
	// callback solves the problem.

	// Make sure uint16_t/uint32_t/uint64_t are defined.
	#include <stdint.h>

	extern "C" {
	uint16_t __sanitizer_unaligned_load16(const void *p);
	uint32_t __sanitizer_unaligned_load32(const void *p);
	uint64_t __sanitizer_unaligned_load64(const void *p);
	void __sanitizer_unaligned_store16(void *p, uint16_t v);
	void __sanitizer_unaligned_store32(void *p, uint32_t v);
	void __sanitizer_unaligned_store64(void *p, uint64_t v);
	} // extern "C"

	namespace absl {

	inline uint16_t UnalignedLoad16(const void *p) {
	return __sanitizer_unaligned_load16(p);
	}

	inline uint32_t UnalignedLoad32(const void *p) {
	return __sanitizer_unaligned_load32(p);
	}

	inline uint64_t UnalignedLoad64(const void *p) {
	return __sanitizer_unaligned_load64(p);
	}

	inline void UnalignedStore16(void *p, uint16_t v) {
	__sanitizer_unaligned_store16(p, v);
	}

	inline void UnalignedStore32(void *p, uint32_t v) {
	__sanitizer_unaligned_store32(p, v);
	}

	inline void UnalignedStore64(void *p, uint64_t v) {
	__sanitizer_unaligned_store64(p, v);
	}

	} // namespace absl

	#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) (absl::UnalignedLoad16(_p))
	#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) (absl::UnalignedLoad32(_p))
	#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))

	#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
	(absl::UnalignedStore16(_p, _val))
	#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
	(absl::UnalignedStore32(_p, _val))
	#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
	(absl::UnalignedStore64(_p, _val))

	#elif defined(__x86_64__) \|\| defined(_M_X64) \|\| defined(__i386) \|\| \
	defined(_M_IX86) \|\| defined(__ppc__) \|\| defined(__PPC__) \|\| \
	defined(__ppc64__) \|\| defined(__PPC64__)

	// x86 and x86-64 can perform unaligned loads/stores directly;
	// modern PowerPC hardware can also do unaligned integer loads and stores;
	// but note: the FPU still sends unaligned loads and stores to a trap handler!

	#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
	(reinterpret_cast<const uint16_t >(_p))
	#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
	(reinterpret_cast<const uint32_t >(_p))
	#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
	(reinterpret_cast<const uint64_t >(_p))

	#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
	(reinterpret_cast<uint16_t >(_p) = (_val))
	#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
	(reinterpret_cast<uint32_t >(_p) = (_val))
	#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
	(reinterpret_cast<uint64_t >(_p) = (_val))

	#elif defined(__arm__) && \
	!defined(__ARM_ARCH_5__) && \
	!defined(__ARM_ARCH_5T__) && \
	!defined(__ARM_ARCH_5TE__) && \
	!defined(__ARM_ARCH_5TEJ__) && \
	!defined(__ARM_ARCH_6__) && \
	!defined(__ARM_ARCH_6J__) && \
	!defined(__ARM_ARCH_6K__) && \
	!defined(__ARM_ARCH_6Z__) && \
	!defined(__ARM_ARCH_6ZK__) && \
	!defined(__ARM_ARCH_6T2__)


	// ARMv7 and newer support native unaligned accesses, but only of 16-bit
	// and 32-bit values (not 64-bit); older versions either raise a fatal signal,
	// do an unaligned read and rotate the words around a bit, or do the reads very
	// slowly (trip through kernel mode). There's no simple #define that says just
	// "ARMv7 or higher", so we have to filter away all ARMv5 and ARMv6
	// sub-architectures. Newer gcc (>= 4.6) set an __ARM_FEATURE_ALIGNED #define,
	// so in time, maybe we can move on to that.
	//
	// This is a mess, but there's not much we can do about it.
	//
	// To further complicate matters, only LDR instructions (single reads) are
	// allowed to be unaligned, not LDRD (two reads) or LDM (many reads). Unless we
	// explicitly tell the compiler that these accesses can be unaligned, it can and
	// will combine accesses. On armcc, the way to signal this is done by accessing
	// through the type (uint32_t __packed *), but GCC has no such attribute
	// (it ignores __attribute__((packed)) on individual variables). However,
	// we can tell it that a _struct_ is unaligned, which has the same effect,
	// so we do that.

	namespace absl {
	namespace internal {

	struct Unaligned16Struct {
	uint16_t value;
	uint8_t dummy; // To make the size non-power-of-two.
	} ABSL_ATTRIBUTE_PACKED;

	struct Unaligned32Struct {
	uint32_t value;
	uint8_t dummy; // To make the size non-power-of-two.
	} ABSL_ATTRIBUTE_PACKED;

	} // namespace internal
	} // namespace absl

	#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
	((reinterpret_cast<const ::absl::internal::Unaligned16Struct *>(_p))->value)
	#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
	((reinterpret_cast<const ::absl::internal::Unaligned32Struct *>(_p))->value)

	#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
	((reinterpret_cast< ::absl::internal::Unaligned16Struct *>(_p))->value = \
	(_val))
	#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
	((reinterpret_cast< ::absl::internal::Unaligned32Struct *>(_p))->value = \
	(_val))

	namespace absl {

	inline uint64_t UnalignedLoad64(const void *p) {
	uint64_t t;
	memcpy(&t, p, sizeof t);
	return t;
	}

	inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }

	} // namespace absl

	#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))
	#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
	(absl::UnalignedStore64(_p, _val))

	#else

	// ABSL_INTERNAL_NEED_ALIGNED_LOADS is defined when the underlying platform
	// doesn't support unaligned access.
	#define ABSL_INTERNAL_NEED_ALIGNED_LOADS

	// These functions are provided for architectures that don't support
	// unaligned loads and stores.

	namespace absl {

	inline uint16_t UnalignedLoad16(const void *p) {
	uint16_t t;
	memcpy(&t, p, sizeof t);
	return t;
	}

	inline uint32_t UnalignedLoad32(const void *p) {
	uint32_t t;
	memcpy(&t, p, sizeof t);
	return t;
	}

	inline uint64_t UnalignedLoad64(const void *p) {
	uint64_t t;
	memcpy(&t, p, sizeof t);
	return t;
	}

	inline void UnalignedStore16(void *p, uint16_t v) { memcpy(p, &v, sizeof v); }

	inline void UnalignedStore32(void *p, uint32_t v) { memcpy(p, &v, sizeof v); }

	inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }

	} // namespace absl

	#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) (absl::UnalignedLoad16(_p))
	#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) (absl::UnalignedLoad32(_p))
	#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) (absl::UnalignedLoad64(_p))

	#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
	(absl::UnalignedStore16(_p, _val))
	#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
	(absl::UnalignedStore32(_p, _val))
	#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
	(absl::UnalignedStore64(_p, _val))

	#endif

	#endif // defined(__cplusplus), end of unaligned API

	#endif // ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_