All Questions
339
questions
0
votes
1
answer
23
views
Alignment problem with UBO on CPU/GPU, GLSL/VULKAN
After adding directional lights to UBO, the light is incorrect on scene. Tried to shuffle elements around, but it doesn't help. If i correct, GLSL UBO structure should be 920 bytes in size? What is ...
- 25
0
votes
0
answers
24
views
getting aligned pointer inside storage to place object
I have a storage in a form of an array of bytes.
On the stack
// storage on the stack, no requirement on alignment
unsigned char storage[N];
Or on the heap
// storage on the heap, no requirement on ...
- 1,706
0
votes
0
answers
39
views
what can be overaligned types
is "Tis overaligned" equivalent to alignof(T)>alignof(std::max_align_t)? And is it possible to have an overaligned type without using alignas keyword or another explicit alignment ...
- 1,706
0
votes
0
answers
31
views
Getting heap storage with proper alignment in C++ for overaligned type
In some use case, you'll need to allocate storage before creating objects inside this storage.
Then in order to create these objects, you may need to use placement new:
T *pobj = new(pstorage);
yet ...
- 1,706
-2
votes
1
answer
64
views
Getting heap storage with proper alignment in C++ for non-overaligned type
In some use case, you'll need to allocate storage before creating objects inside this storage.
Then in order to create these objects, you may need to use placement new:
T *pobj = new(pstorage);
yet ...
- 1,706
2
votes
1
answer
83
views
Correctly deleting a dynamically allocated plain array, allocated with `std::align_val_t` alignment parameter
As an answer to Idiom for initializing an std::array using a generator function taking the index?, I proposed a way to obtain a properly aligned storage.
Yet I think that my solution can be simplified,...
- 1,706
1
vote
1
answer
75
views
How to know the size of an aligned type including padding
I have a buffer with chunks that align to the cacheline size, but have arbitrary length, let's say 100 bytes. It is clear to me that the buffer (vector) elements are aligned on cacheline borders, but ...
- 4,475
1
vote
1
answer
38
views
C++ rebind allocator with two template parameter
I'm writing an allocator that takes alignment as a template parameter also the alignment:
template<typename T, std::align_val_t alignment>
class AlignedAllocator {
public:
using value_type = T;...
- 683
1
vote
2
answers
106
views
Why is the size of this subclass the same as the base class even though it adds a member variable?
In the following code, why is the size of Parent the same as the size of Child (even though Child adds a member variable)? Another weird behaviour: if I comment out the line where b is defined, the ...
- 17
1
vote
0
answers
68
views
Using placement new on underaligned buffer in C++
Given a buffer
char buf[sizeof(T) + alignof(T) - 1];
Is calling placement new that constructs an instance of T on the pointer to the first element of buf that is located at an address which is a ...
1
vote
1
answer
50
views
Converting a templated data into another templated data
I have a method returning a templated class and taking as argument another templated class such as :
template <class T, class U>
T caster(U* u)
{
return reinterpret_cast<T>(u);
}
...
- 87
7
votes
3
answers
442
views
How to control the size of a class to be a multiple of the size of a member?
I have the following class,
struct employee {
std::string name;
short salary;
std::size_t age;
};
Just as an example, in Linux amd64, the size of the struct is 48 bytes, and the size of ...
- 15.6k
2
votes
1
answer
116
views
C++: Is there ever a reason to make alignof > sizeof for a type
As indicated in this question, it is possible to have alignment greater than size for a type, you just can't make an array of it.
However you can make an array of char[alignof(T)] and reinterpret_cast ...
- 2,080
0
votes
0
answers
66
views
why did the align addresses have gaps (c++)?
#include <iostream>
using namespace std;
int main() {
alignas(0x10000) int ptr[42];
cout << ptr << endl;
if (auto ptr = aligned_alloc(0x1000, 42 * sizeof(int))) {
cout &...
- 1
0
votes
1
answer
148
views
Why memory alignment of structs that contain arrays of type T is always 1
I was exploring memory alignment and padding, and thought that I got the hang of it until I came across this:
struct Example {
int x1; // 4
char c; // 1 + 3 padding
int x2; // 4
};
...
- 107