50
votes
3
answers
1.8K
views
Why does GCC generate such radically different assembly for nearly the same C code?
While writing an optimized ftol function I found some very odd behaviour in GCC 4.6.1. Let me show you the cod
64
votes
11
answers
1.9K
views
Replacing a 32-bit loop counter with 64-bit introduces crazy performance deviations with _mm_popcnt_u64 on Intel CPUs
I was looking for the fastest way to popcount large arrays of data. I encountered a very weird effect: Changin
58
votes
12
answers
932
views
Why doesn't GCC optimize a*a*a*a*a*a to (a*a*a)*(a*a*a)?
I am doing some numerical optimization on a scientific application. One thing I noticed is that GCC will optim
51
votes
9
answers
2.7K
views
Swift Beta performance: sorting arrays
I was implementing an algorithm in Swift Beta and noticed that the performance was very poor. After digging de
