A branch instruction is not inherently slower than any other instruction. However, the reason you heard that branches should avoided is because modern CPUs follow a pipeline architecture. This means that there are multiple sequential instructions being executed simultaneously. But the pipeline can only be fully utilised if it’s able to read the next instruction … Read more
I developed this answer after following a link from dmckee’s answer, but it takes a different approach than his/her answer. Function Attributes documentation from GCC mentions: noinline This function attribute prevents a function from being considered for inlining. If the function does not have side-effects, there are optimizations other than inlining that causes function calls … Read more
The most likely cause of the speed improvement is that: inserting a MOV shifts the subsequent instructions to different memory addresses one of those moved instructions was an important conditional branch that branch was being incorrectly predicted due to aliasing in the branch prediction table moving the branch eliminated the alias and allowed the branch … Read more
Sure thing. It knows the value of function is the same as the value it passes it, knows the definition of the function, so just replaces the definition inline and calls the function directly. I can’t think of a condition where a compiler won’t inline a one-line function call, it’s just replacing a function call … Read more
There are cases where the same algorithm will optimize better in a pure context. Specifically, stream fusion allows an algorithm that consists of a sequence of loops that may be of widely varying form: maps, filters, folds, unfolds, to be composed into a single loop. The equivalent optimization in a conventional imperative setting, with mutable … Read more
We can have our cake and eat it to, too. Let’s just consider the simplest specialization of copy, the one that copies chars. In C++17, that might look like: char* copy(char const* first, char const* last, char* d) { memcpy(d, first, last – first); return d + (last – first); } Of course, we can’t … Read more
This avoids looping: int tmp = a % b; if (tmp < 0) tmp += b; Notice that both a and b need to be signed.
This may be helpful: https://code.google.com/p/find-unused-classes/ . According to the description: It shows classes that exist in css selectors and do not exist on html page and like-verse. As Jim said, be warned that some classes may be unused by your stylesheets but still used in JavaScript.
To answer the question in the title – as mentioned by others, containsValue is O(n), because without the key it doesn’t know where it is and the algorithm has to go over all the values stored in the map. To answer the question in the body of your question – on how to solve it … Read more