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mdbx++: упрощение buffer:silo::inplace_signature.

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Леонид Юрьев (Leonid Yuriev) 2024-05-04 21:42:53 +03:00
parent 95bc96dda3
commit e9f5c0c308
1 changed files with 16 additions and 24 deletions
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40
mdbx.h++
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@ -1734,24 +1734,13 @@ private:
return capacity_bytes < sizeof(bin);
}
enum : byte {
/* Little Endian:
* last byte is the most significant byte of u_.allocated.cap,
* so use higher bit of capacity as the inplace-flag */
le_lastbyte_mask = 0x80,
/* Big Endian:
* last byte is the least significant byte of u_.allocated.cap,
* so use lower bit of capacity as the inplace-flag. */
be_lastbyte_mask = 0x01
enum : byte { lastbyte_inplace_signature = byte(~0u) };
enum : size_t {
inplace_signature_limit =
size_t(lastbyte_inplace_signature)
<< (sizeof(size_t /* allocated::capacity_bytes_ */) - 1) * CHAR_BIT
};
static constexpr byte inplace_lastbyte_mask() noexcept {
static_assert(
endian::native == endian::little || endian::native == endian::big,
"Only the little-endian or big-endian bytes order are supported");
return (endian::native == endian::little) ? le_lastbyte_mask
: be_lastbyte_mask;
}
constexpr byte lastbyte() const noexcept {
return inplace_[sizeof(bin) - 1];
}
@ -1760,7 +1749,14 @@ private:
}
constexpr bool is_inplace() const noexcept {
return (lastbyte() & inplace_lastbyte_mask()) != 0;
static_assert(size_t(inplace_signature_limit) > size_t(max_capacity),
"WTF?");
static_assert(
std::numeric_limits<size_t>::max() -
(std::numeric_limits<size_t>::max() >> CHAR_BIT) ==
inplace_signature_limit,
"WTF?");
return lastbyte() == lastbyte_inplace_signature;
}
constexpr bool is_allocated() const noexcept { return !is_inplace(); }
@ -1773,8 +1769,8 @@ private:
}
if (::std::is_trivial<allocator_pointer>::value)
/* workaround for "uninitialized" warning from some compilers */
::std::memset(&allocated_.ptr_, 0, sizeof(allocated_.ptr_));
lastbyte() = inplace_lastbyte_mask();
memset(&allocated_.ptr_, 0, sizeof(allocated_.ptr_));
lastbyte() = lastbyte_inplace_signature;
MDBX_CONSTEXPR_ASSERT(is_inplace() && address() == inplace_ &&
is_suitable_for_inplace(capacity()));
return address();
@ -1783,11 +1779,7 @@ private:
template <bool construct_ptr>
MDBX_CXX17_CONSTEXPR byte *
make_allocated(allocator_pointer ptr, size_t capacity_bytes) noexcept {
MDBX_CONSTEXPR_ASSERT(
(capacity_bytes & be_lastbyte_mask) == 0 &&
((capacity_bytes >>
(sizeof(allocated_.capacity_bytes_) - 1) * CHAR_BIT) &
le_lastbyte_mask) == 0);
MDBX_CONSTEXPR_ASSERT(inplace_signature_limit > capacity_bytes);
if (construct_ptr)
/* properly construct allocator::pointer */
new (&allocated_) allocated(ptr, capacity_bytes);