As a general rule, most if not all Intel CPUs assume forward branches are not taken the first time they see them. See Godbolt’s work. After that, the branch goes into a branch prediction cache, and past behavior is used to inform future branch prediction. So in a tight loop, the effect of misordering is … Read more
Why is creating a Thread said to be expensive? Because it >>is<< expensive. Java thread creation is expensive because there is a fair bit of work involved: A large block of memory has to be allocated and initialized for the thread stack. System calls need to be made to create / register the native thread … Read more
It shouldn’t have any discernible effects on performance. Seeing Firefox’s CSS parser at /source/layout/style/nsCSSDataBlock.cpp#572 and I think that is the relevant routine, handling overwriting of CSS rules. It just seems to be a simple check for “important”. if (aIsImportant) { if (!HasImportantBit(aPropID)) changed = PR_TRUE; SetImportantBit(aPropID); } else { // … } Also, comments at … Read more
EXISTS (or NOT EXISTS) is specially designed for checking if something exists and therefore should be (and is) the best option. It will halt on the first row that matches so it does not require a TOP clause and it does not actually select any data so there is no overhead in size of columns. … Read more
The async support as specified by google is achieved using two parts: using script on your page (the script is supplied by google) to write out a <script> tag to the DOM. that script has async=”true” attribute to signal to compatible browsers that it can continue rendering the page. The first part works on browsers … Read more
-ffast-math does a lot more than just break strict IEEE compliance. First of all, of course, it does break strict IEEE compliance, allowing e.g. the reordering of instructions to something which is mathematically the same (ideally) but not exactly the same in floating point. Second, it disables setting errno after single-instruction math functions, which means … Read more
As many others have alluded, the comparison lacks context. At the time of its release, the async approach of node.js was revolutionary. Since then other languages and web frameworks have been adopting the approaches they took mainstream. To understand what the difference meant, you need to simulate a blocking request that represents some IO workload, … Read more
I’m going to go against the general wisdom here that std::copy will have a slight, almost imperceptible performance loss. I just did a test and found that to be untrue: I did notice a performance difference. However, the winner was std::copy. I wrote a C++ SHA-2 implementation. In my test, I hash 5 strings using … Read more
Here’s some advice from someone with an environment where we have folders containing tens of millions of files. A folder stores the index information (links to child files & child folder) in an index file. This file will get very large when you have a lot of children. Note that it doesn’t distinguish between a … Read more
This kind of question is recurring and should be answered more clearly than “MATLAB uses highly optimized libraries” or “MATLAB uses the MKL” for once on Stack Overflow. History: Matrix multiplication (together with Matrix-vector, vector-vector multiplication and many of the matrix decompositions) is (are) the most important problems in linear algebra. Engineers have been solving … Read more