std::aligned_alloc and aligned operator new in C++ 17
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I have questions regarding the std::aligned_alloc and aligned operator new in C++ 17.
Do I understand correctly that the aligned version of operator new works only on the oblects that were declared as aligned? i.e
struct alignas(16) aligned_shorts
{
short shorts[8];
};
Only then new aligned_shorts[7] will result in aligned memory?
But what if I want a aligned dynamic array i. e of ints?
int *aligned_ints;// want aligned dynamic array
Can be std::aligned_alloc used for that? And if I need to overalign (e. g. for vectorization) I would need to overallocate/pad:
int* allocate_aligned_ints(int num, int align_as)
{
int needed_memory=num*sizeof(int);
if((needed_memory% align_as) > 0)//
needed_memory+=(align_as- needed_memory% align_as);//pad if neccessary
return static_cast<int*>(std::aligned_alloc(align_as, needed_memory));
}
memory-management c++17 memory-alignment
asked Nov 26 '18 at 16:47
Andrey ProAndrey Pro
256217
add a comment |
I have questions regarding the std::aligned_alloc and aligned operator new in C++ 17.
Do I understand correctly that the aligned version of operator new works only on the oblects that were declared as aligned? i.e
struct alignas(16) aligned_shorts
{
short shorts[8];
};
Only then new aligned_shorts[7] will result in aligned memory?
But what if I want a aligned dynamic array i. e of ints?
int *aligned_ints;// want aligned dynamic array
Can be std::aligned_alloc used for that? And if I need to overalign (e. g. for vectorization) I would need to overallocate/pad:
int* allocate_aligned_ints(int num, int align_as)
{
int needed_memory=num*sizeof(int);
if((needed_memory% align_as) > 0)//
needed_memory+=(align_as- needed_memory% align_as);//pad if neccessary
return static_cast<int*>(std::aligned_alloc(align_as, needed_memory));
}
memory-management c++17 memory-alignment
asked Nov 26 '18 at 16:47
Andrey ProAndrey Pro
256217
1
"I would need to overallocate/pad a bit" Why wouldstd::aligned_alloceven exist if you needed to do that?
– Nicol Bolas
Nov 26 '18 at 17:02
@NicolBolas I had overalignment in mind. Clarified that with the edit.
– Andrey Pro
Nov 26 '18 at 18:02
I'm confused, why not just usestd::aligned_alloc(align_as, needed_memory)? Why the explict 16 in your example?
– Frank
Nov 26 '18 at 20:37
@Frank you are right, inattention on my part. Corrected.
– Andrey Pro
Nov 26 '18 at 21:27
add a comment |
I have questions regarding the std::aligned_alloc and aligned operator new in C++ 17.
Do I understand correctly that the aligned version of operator new works only on the oblects that were declared as aligned? i.e
struct alignas(16) aligned_shorts
{
short shorts[8];
};
Only then new aligned_shorts[7] will result in aligned memory?
But what if I want a aligned dynamic array i. e of ints?
int *aligned_ints;// want aligned dynamic array
Can be std::aligned_alloc used for that? And if I need to overalign (e. g. for vectorization) I would need to overallocate/pad:
int* allocate_aligned_ints(int num, int align_as)
{
int needed_memory=num*sizeof(int);
if((needed_memory% align_as) > 0)//
needed_memory+=(align_as- needed_memory% align_as);//pad if neccessary
return static_cast<int*>(std::aligned_alloc(align_as, needed_memory));
}
memory-management c++17 memory-alignment
asked Nov 26 '18 at 16:47
Andrey ProAndrey Pro
256217
I have questions regarding the std::aligned_alloc and aligned operator new in C++ 17.
Do I understand correctly that the aligned version of operator new works only on the oblects that were declared as aligned? i.e
struct alignas(16) aligned_shorts
{
short shorts[8];
};
Only then new aligned_shorts[7] will result in aligned memory?
But what if I want a aligned dynamic array i. e of ints?
int *aligned_ints;// want aligned dynamic array
Can be std::aligned_alloc used for that? And if I need to overalign (e. g. for vectorization) I would need to overallocate/pad:
int* allocate_aligned_ints(int num, int align_as)
{
int needed_memory=num*sizeof(int);
if((needed_memory% align_as) > 0)//
needed_memory+=(align_as- needed_memory% align_as);//pad if neccessary
return static_cast<int*>(std::aligned_alloc(align_as, needed_memory));
}
memory-management c++17 memory-alignment
memory-management c++17 memory-alignment
asked Nov 26 '18 at 16:47
Andrey ProAndrey Pro
256217
asked Nov 26 '18 at 16:47
Andrey ProAndrey Pro
256217
edited Nov 26 '18 at 21:26
Andrey Pro
asked Nov 26 '18 at 16:47
Andrey ProAndrey Pro
256217
asked Nov 26 '18 at 16:47
Andrey ProAndrey Pro
256217
asked Nov 26 '18 at 16:47
Andrey ProAndrey Pro
256217
256217
1
"I would need to overallocate/pad a bit" Why wouldstd::aligned_alloceven exist if you needed to do that?
– Nicol Bolas
Nov 26 '18 at 17:02
@NicolBolas I had overalignment in mind. Clarified that with the edit.
– Andrey Pro
Nov 26 '18 at 18:02
I'm confused, why not just usestd::aligned_alloc(align_as, needed_memory)? Why the explict 16 in your example?
– Frank
Nov 26 '18 at 20:37
@Frank you are right, inattention on my part. Corrected.
– Andrey Pro
Nov 26 '18 at 21:27
add a comment |
1
"I would need to overallocate/pad a bit" Why wouldstd::aligned_alloceven exist if you needed to do that?
– Nicol Bolas
Nov 26 '18 at 17:02
@NicolBolas I had overalignment in mind. Clarified that with the edit.
– Andrey Pro
Nov 26 '18 at 18:02
I'm confused, why not just usestd::aligned_alloc(align_as, needed_memory)? Why the explict 16 in your example?
– Frank
Nov 26 '18 at 20:37
@Frank you are right, inattention on my part. Corrected.
– Andrey Pro
Nov 26 '18 at 21:27
1
1
"I would need to overallocate/pad a bit" Why would
std::aligned_alloc even exist if you needed to do that?– Nicol Bolas
Nov 26 '18 at 17:02
"I would need to overallocate/pad a bit" Why would
std::aligned_alloc even exist if you needed to do that?– Nicol Bolas
Nov 26 '18 at 17:02
@NicolBolas I had overalignment in mind. Clarified that with the edit.
– Andrey Pro
Nov 26 '18 at 18:02
@NicolBolas I had overalignment in mind. Clarified that with the edit.
– Andrey Pro
Nov 26 '18 at 18:02
I'm confused, why not just use
std::aligned_alloc(align_as, needed_memory)? Why the explict 16 in your example?– Frank
Nov 26 '18 at 20:37
I'm confused, why not just use
std::aligned_alloc(align_as, needed_memory)? Why the explict 16 in your example?– Frank
Nov 26 '18 at 20:37
@Frank you are right, inattention on my part. Corrected.
– Andrey Pro
Nov 26 '18 at 21:27
@Frank you are right, inattention on my part. Corrected.
– Andrey Pro
Nov 26 '18 at 21:27
add a comment |
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1
"I would need to overallocate/pad a bit" Why would
std::aligned_alloceven exist if you needed to do that?– Nicol Bolas
Nov 26 '18 at 17:02
@NicolBolas I had overalignment in mind. Clarified that with the edit.
– Andrey Pro
Nov 26 '18 at 18:02
I'm confused, why not just use
std::aligned_alloc(align_as, needed_memory)? Why the explict 16 in your example?– Frank
Nov 26 '18 at 20:37
@Frank you are right, inattention on my part. Corrected.
– Andrey Pro
Nov 26 '18 at 21:27