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I'm trying to find the source of performance issues with my application. Using Visual Studio 2017 profiling tools I got this result:
I'm relatively new to C++ so I'm not sure what this std::vector<bool,std::allocator<bool> >::operator[] stuff is or if this is really the bottleneck in my program or not. Any help is appreciated.
Here is my code:
https://github.com/k-vekos/GameOfLife/tree/multithread
In a game of life, what you do is read state to make decisions. So sure, that is most of the time.
Your access is near random due to your std vector of std vector in virtual address space. A single buffer, with a vector of spans, would improve memory locality significantly.
If you keep a 0 or 1 in those locations, doing += instead of a branch might help.
Also vector of bool is packed bits; this makes access slower. Vector of single bytes could be faster with your simpke algorithm.
Note that fancy games of life do zone based hashing to skip frames in large areas.
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I was hoping someone had some schooling they could lay down about the whole HEAP and stack ordeal. I am trying to make a program that would attempt to create about 20,000 instances of just one union and if so some day I may want to implement a much larger program. Other than my current project consisting of a maximum of just 20,000 unions stored where ever c++ will allocate them do you think I could up the anti into the millions while retaining a reasonable return speed on function calls, approximately 1,360,000 or so? And how do you think it will handle 20,000?
Heap is an area used for dynamic memory allocation.
It's usually used to allocate space for variable collection size, and/or to allocate a large amount of memory. It's definitely not a CPU register(s).
Besides this I think there is no guarantee what heap is.
This may be RAM, may be processor cache, even HDD storage. Let OS and hardware decide what it will be in particular case.
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Some days ago I wanted to use C++ sort() function to sort an array of strings, but I had a problem!
What algorithm does it use to sort the array? Is it a deterministic one or may it use different algorithms based on the type of the array?
Also, is there a clear time complexity analysis about it?
Does this function use the same algorithm for sorting numbers array and strings array?
It might or it might not. That is not specified by the standard.
And if we use it to sort an array of strings which the total size of them is less than 100,000 characters, would it work in less than 1 second(in the worst case)?
It might or it might not. It depends on the machine you're running the program on. Even if it will work in less than 1 second in worst case on a particular machine, it would be difficult to prove. But you can get a decent estimation by measuring. A measurement only applies to the machine it was performed, of course.
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I'm still new to C++ but I catch on quick and also have experience in C#. Something I want to know is, what are some performance safe actions I can take to ensure that my game runs efficiently. Also, in which scenario am I likely to run out of memory on. 2k to 3k bullet objects on the stack, or heap? I think the stack is generally faster, but I heard that too much causes a stack overflow. That being said, how much is too much exactly?
Sorry for the plethora of questions, I just want to make sure I don't design a game engine in which it relies on good PCs in order to run well.
Firstly, program your game safely and only worry about optimizations like memory layout after profiling & debugging.
That being said, I have to dispel the myth that the stack is faster than the heap. What matters is cache performance.
The stack generally is faster for small quick accesses, because the stack usually already is in the cache. But when you are iterating over thousands of bullet objects on the heap, as long as you store them contiguously (e.g. std::vector, not std::list), everything should be loaded into the cache, and there should be no performance difference.
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I was doing some work handling a lot of information and my partner told me that I was using too many matrices to manipulate the variables of the problem. The idea was to use one dimension arrays int a[] instead of the 2 dimensional arrays int b[][], to save memory and processing speed of the algorithm. How certain is that this change will accelerate the speed of execution or compilation of my code in c ++?
Your question invites to guesswork, but:
How certain is that this change will accelerate the speed of execution or compilation of my code in c ++?
Prognosis is extremely uncertain. The only proper response is to measure.
Measuring is knowing. You can quote me on that.
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In theory memory circularBuffer sounds like a good idea... the setting and the getting are never at the same address. However the limiting factor in the hardware. The computer will only allow use to access one memory location at a time. So then how can a circularBuffer improve performance ??
This link gives some reasons why circular buffers offer better performance than synchronized access to a single, shared data structure.
What hardware are you using, that only allows access to one memory location at a time?