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vector_algorithms.cpp: avoid unaligned access #5760

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Merged
Stephan T. Lavavej (StephanTLavavej) merged 1 commit into from
Oct 10, 2025
Merged

vector_algorithms.cpp: avoid unaligned access #5760

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58 changes: 34 additions & 24 deletions stl/src/vector_algorithms.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -111,30 +111,34 @@ __declspec(noalias) void __cdecl __std_swap_ranges_trivially_swappable_noalias(
} while (_First1 != _Stop_at);
}

#if defined(_M_X64) // NOTE: UNALIGNED MEMORY ACCESSES
#if defined(_M_X64)
constexpr size_t _Mask_8 = ~((static_cast<size_t>(1) << 3) - 1);
if (_Byte_length(_First1, _Last1) >= 8) {
const void* _Stop_at = _First1;
_Advance_bytes(_Stop_at, _Byte_length(_First1, _Last1) & _Mask_8);
do {
const unsigned long long _Left = *static_cast<unsigned long long*>(_First1);
const unsigned long long _Right = *static_cast<unsigned long long*>(_First2);
*static_cast<unsigned long long*>(_First1) = _Right;
*static_cast<unsigned long long*>(_First2) = _Left;
unsigned long long _Left;
unsigned long long _Right;
memcpy(&_Left, _First1, 8);
memcpy(&_Right, _First2, 8);
memcpy(_First1, &_Right, 8);
memcpy(_First2, &_Left, 8);
_Advance_bytes(_First1, 8);
_Advance_bytes(_First2, 8);
} while (_First1 != _Stop_at);
}
#elif defined(_M_IX86) // NOTE: UNALIGNED MEMORY ACCESSES
#elif defined(_M_IX86)
constexpr size_t _Mask_4 = ~((static_cast<size_t>(1) << 2) - 1);
if (_Byte_length(_First1, _Last1) >= 4) {
const void* _Stop_at = _First1;
_Advance_bytes(_Stop_at, _Byte_length(_First1, _Last1) & _Mask_4);
do {
const unsigned long _Left = *static_cast<unsigned long*>(_First1);
const unsigned long _Right = *static_cast<unsigned long*>(_First2);
*static_cast<unsigned long*>(_First1) = _Right;
*static_cast<unsigned long*>(_First2) = _Left;
unsigned long _Left;
unsigned long _Right;
memcpy(&_Left, _First1, 4);
memcpy(&_Right, _First2, 4);
memcpy(_First1, &_Right, 4);
memcpy(_First2, &_Left, 4);
_Advance_bytes(_First1, 4);
_Advance_bytes(_First2, 4);
} while (_First1 != _Stop_at);
Expand Down Expand Up @@ -202,35 +206,41 @@ namespace {
} while (_First1 != _Stop_at);
}

#if defined(_M_X64) // NOTE: UNALIGNED MEMORY ACCESSES
#if defined(_M_X64)
constexpr size_t _Mask_8 = ~((static_cast<size_t>(1) << 3) - 1);
if (_Byte_length(_First1, _Last1) >= 8) {
const void* _Stop_at = _First1;
_Advance_bytes(_Stop_at, _Byte_length(_First1, _Last1) & _Mask_8);
do {
const unsigned long long _Val1 = *static_cast<unsigned long long*>(_First1);
const unsigned long long _Val2 = *static_cast<unsigned long long*>(_First2);
const unsigned long long _Val3 = *static_cast<unsigned long long*>(_First3);
*static_cast<unsigned long long*>(_First1) = _Val2;
*static_cast<unsigned long long*>(_First2) = _Val3;
*static_cast<unsigned long long*>(_First3) = _Val1;
unsigned long long _Val1;
unsigned long long _Val2;
unsigned long long _Val3;
memcpy(&_Val1, _First1, 8);
memcpy(&_Val2, _First2, 8);
memcpy(&_Val3, _First3, 8);
memcpy(_First1, &_Val2, 8);
memcpy(_First2, &_Val3, 8);
memcpy(_First3, &_Val1, 8);
_Advance_bytes(_First1, 8);
_Advance_bytes(_First2, 8);
_Advance_bytes(_First3, 8);
} while (_First1 != _Stop_at);
}
#elif defined(_M_IX86) // NOTE: UNALIGNED MEMORY ACCESSES
#elif defined(_M_IX86)
constexpr size_t _Mask_4 = ~((static_cast<size_t>(1) << 2) - 1);
if (_Byte_length(_First1, _Last1) >= 4) {
const void* _Stop_at = _First1;
_Advance_bytes(_Stop_at, _Byte_length(_First1, _Last1) & _Mask_4);
do {
const unsigned long _Val1 = *static_cast<unsigned long*>(_First1);
const unsigned long _Val2 = *static_cast<unsigned long*>(_First2);
const unsigned long _Val3 = *static_cast<unsigned long*>(_First3);
*static_cast<unsigned long*>(_First1) = _Val2;
*static_cast<unsigned long*>(_First2) = _Val3;
*static_cast<unsigned long*>(_First3) = _Val1;
unsigned long _Val1;
unsigned long _Val2;
unsigned long _Val3;
memcpy(&_Val1, _First1, 4);
memcpy(&_Val2, _First2, 4);
memcpy(&_Val3, _First3, 4);
memcpy(_First1, &_Val2, 4);
memcpy(_First2, &_Val3, 4);
memcpy(_First3, &_Val1, 4);
_Advance_bytes(_First1, 4);
_Advance_bytes(_First2, 4);
_Advance_bytes(_First3, 4);
Expand Down