Yes, semantically it will be evaluated on every loop. In some cases, compilers may be able to remove the condition from the loop automatically – but not always. In particular: void foo(const struct rect *r) { for (int i = 0; i < r->width * r->height; i++) { quux(); } } The compiler will not … Read more
Performance As has been suggested in previous answers, use of the inline keyword can make code faster by inlining function calls, often at the expense of increased executables. “Inlining function calls” just means substituting the call to the target function with the actual code of the function, after filling in the arguments accordingly. However, modern … Read more
That would be true if you are working on a “stone-age” compiler… In case of “stone-age”: ++n is faster than n++ is faster than n=n+1 Machine usually have increment x as well as add const to x In case of n++, you will have 2 memory access only (read n, inc n, write n ) … Read more
You are using an unsigned 32-bits type for the array index (on line 21). This forces the compiler to consider at each step through the loop whether you might have overflowed its available range, in which case it needs to go back to the beginning of the array. The extra code you see is related … Read more
NOTE! This answer was written before the rotation requirement. Proceed at your own caution 🙂 Here’s my initial look at the problem. The first thing to do is calculate the parity of the exterior – +1 if it would fit ‘stripes in corners’, -1 if it would fit ‘solids in corners’, +0 if it’s the … Read more
Newer microarchitectures have shifted the odds towards gather instructions. On an Intel Xeon Gold 6138 CPU @ 2.00 GHz with Skylake microarchitecture, we get for your benchmark: 9.383e+09 8.86e+08 2.777e+09 6.915e+09 7.793e+09 8.335e+09 5.386e+09 4.92e+08 6.649e+09 1.421e+09 2.362e+09 2.7e+07 8.69e+09 5.9e+07 7.763e+09 3.926e+09 5.4e+08 3.426e+09 9.172e+09 5.736e+09 9.383e+09 8.86e+08 2.777e+09 6.915e+09 7.793e+09 8.335e+09 5.386e+09 4.92e+08 … Read more
Here are some good slides on how to do power series approximations (NOT Taylor series though) of trig functions: Faster Math Functions. It’s geared towards game programmers, which means accuracy gets sacrificed for performance, but you should be able to add another term or two to the approximations to get some of the accuracy back. … Read more
The copy constructor exists to make copies. In theory when you write a line like: CLASS c(foo()); The compiler would have to call the copy constructor to copy the return of foo() into c. Copy elision is a technique to skip calling the copy constructor so as not to pay for the overhead. For example, … Read more
I think you’ve answered your own question pretty clearly. For production, we do – as well as most companies I’ve worked with option 3. Here are advantages of solution 3, and why I think you should use it: It utilizes the most caching, all common functionality is loaded once. Taking the least traffic and generating … Read more
I have been studying measuring memory bandwidth for Intel processors with various operations and one of them is memcpy. I have done this on Core2, Ivy Bridge, and Haswell. I did most of my tests using C/C++ with intrinsics (see the code below – but I’m currently rewriting my tests in assembly). To write your … Read more