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mdbx: rework unaligned access.

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The three points:
 - disentangle C11-atomic fences/barriers and pure-functions (with `__attribute__((__pure__))`) to avoid compiler misoptimization;
 - fix hypotetic unaligned access to 64-bit dwords on ARM with `__ARM_FEATURE_UNALIGNED` defined;
 - reasonable paranoia that makes clarity for code readers.
This commit is contained in:
Леонид Юрьев (Leonid Yuriev)
2022-02-09 13:30:23 +03:00
parent cbbfaf3202
commit ef7b4289c0
3 changed files with 125 additions and 60 deletions
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44
test/utils.h
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@@ -148,35 +148,31 @@ static __inline uint16_t bswap16(uint16_t v) { return v << 8 | v >> 8; }
namespace unaligned {
template <typename T> static __inline T load(const void *ptr) {
#if defined(_MSC_VER) && \
(defined(_M_ARM64) || defined(_M_X64) || defined(_M_IA64))
return *(const T __unaligned *)ptr;
#elif MDBX_UNALIGNED_OK
return *(const T *)ptr;
if (MDBX_UNALIGNED_OK >= sizeof(T))
return *(const T *)ptr;
else {
#if defined(__unaligned) || defined(_M_ARM) || defined(_M_ARM64) || \
defined(_M_X64) || defined(_M_IA64)
return *(const T __unaligned *)ptr;
#else
T local;
#if defined(__GNUC__) || defined(__clang__)
__builtin_memcpy(&local, (const T *)ptr, sizeof(T));
#else
memcpy(&local, (const T *)ptr, sizeof(T));
#endif /* __GNUC__ || __clang__ */
return local;
#endif /* MDBX_UNALIGNED_OK */
T local;
memcpy(&local, (const T *)ptr, sizeof(T));
return local;
#endif /* _MSC_VER || __unaligned */
}
}
template <typename T> static __inline void store(void *ptr, const T &value) {
#if defined(_MSC_VER) && \
(defined(_M_ARM64) || defined(_M_X64) || defined(_M_IA64))
*((T __unaligned *)ptr) = value;
#elif MDBX_UNALIGNED_OK
*(volatile T *)ptr = value;
if (MDBX_UNALIGNED_OK >= sizeof(T))
*(T *)ptr = value;
else {
#if defined(__unaligned) || defined(_M_ARM) || defined(_M_ARM64) || \
defined(_M_X64) || defined(_M_IA64)
*((T __unaligned *)ptr) = value;
#else
#if defined(__GNUC__) || defined(__clang__)
__builtin_memcpy(ptr, &value, sizeof(T));
#else
memcpy(ptr, &value, sizeof(T));
#endif /* __GNUC__ || __clang__ */
#endif /* MDBX_UNALIGNED_OK */
memcpy(ptr, &value, sizeof(T));
#endif /* _MSC_VER || __unaligned */
}
}
} /* namespace unaligned */