According to JavaScript Performance for Madmen Wrapping integer arithmetic expressions in ( ) | 0 allows the runtime to be sure that you’re doing integer arithmetic instead of floating-point arithmetic. This allows it to avoid checking for overflow and produce faster code in many cases. and according to the page, it’s true for “most” Javascript … Read more
Flags to use: -s like you’ve been doing to strip symbols -lstdc++_s to specify dynamically linking against the libstdc++.dll -Os to optimize the binary for size. By default mingw static links to libstdc++.a on Windows. Note that the lstdc++_s flag is only in MinGW with GCC > 4.4, I believe.
Re-posting a modified version of my answer from optimized sum of an array of doubles in C, since that question got voted down to -5. The OP of the other question phrased it more as “what else is possible”, so I took him at his word and info-dumped about vectorizing and tuning for current CPU … Read more
AFAICT, the intrinsic leaves garbage in index when the input is zero, weaker than the behaviour of the asm instruction. This is why it has a separate boolean return value and integer output operand. Despite the index arg being taken by reference, the compiler treats it as output-only. unsigned char _BitScanReverse64 (unsigned __int32* index, unsigned … Read more
The reason that it spends so much time in that line is because the Contains method loops through the array to look for the character. Put the characters in a HashSet<char> instead: private static HashSet<char> badChars = new HashSet<char>(new char[] { ‘\x00’, ‘\x09’, ‘\x0A’, ‘\x10’ }); The code to check if the set contains the … Read more
If you are using MongoDB 4.2, you can use aggregation operators in your update statement, like: .findOneAndUpdate({_id: day.id},[{$set:{present:{$eq:[false,”$present”]}}}]); That will set present to true if it is false, and to false if it is any other value.
“should be” is a hazardous thing to say of database performance. I have often found that temp tables speed things up, sometimes dramatically. The simple explanation is that it makes it easier for the optimiser to avoid repeating work. Of course, I’ve also seen temp tables make things slower, sometimes much slower. There is no … Read more
Yes: use Python 3.5 (which is still currently a RC, but should be out momentarily). In Python 3.5, os.walk was rewritten to be more efficient. This work done as part of PEP 471. Extracted from the PEP: Python’s built-in os.walk() is significantly slower than it needs to be, because — in addition to calling os.listdir() … Read more
This is a pretty deep rabbit hole, and I don’t know if I’ve explored all of its twists and turns yet. But here’s a first draft of an answer; suggestions for improvement are welcome. At its core, the culprit is the so-called “fused multiply-add” (or, in this case, a fused multiply-subtract). Fused multiply-add is a … Read more
Fastest way? I’d use something like this: template <class T> constexpr T make_mask(std::size_t pos, std::size_t len) { return ((static_cast<T>(1) << len)-1) << pos; }