Questions
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Faster algorithm for max(ctz(x), ctz(y))?
13 For min(ctz(x), ctz(y)), we can use ctz(x | y) to gain better performance. But what about max(ctz(x), ctz(y))? ctz represents "count trailing zeros". C++ Version (Compiler Explorer) #include <algorithm> #include <bit> #include <cstdint> int32_t test2(uint64_t x, uint64_t y) { return std::max(std::countr_zero(x), std::countr_zero(y)); } Rust Version (Compiler Explorer) pub fn test2(x: u64, y: u64) -> […]
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Efficiently match all values of a vector in another vector
11 I’m looking to find an efficient method of matching all values of vector x in vector y rather than just the first position, as is returned by match(). What I’m after essentially is the default behavior of pmatch() but without partial matching: x <- c(3L, 1L, 2L, 3L, 3L, 2L) y <- c(3L, 3L, […]
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Repeat rows in DataFrame with respect to column
7 I have a Pandas DataFrame that looks like this: df = pd.DataFrame({‘col1’: [1, 2, 3], ‘col2’: [4, 5, 6], ‘col3’: [7, 8, 9]}) df col1 col2 col3 0 1 4 7 1 2 5 8 2 3 6 9 I would like to create a Pandas DataFrame like this: df_new col1 col2 col3 0 […]
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Why in C# an explicit decimal => long conversion operator is called implicitly, losing precision?
6 The following C# program silently and implicitly calls an explicit decimal-to-long conversion operator, losing precision. I don’t understand why this happens. As far as I understand, in C# explicit operator should not be called implicitly by the language. Especially that in this case the silent explicit conversion is losing precision (1.1M => 1L). This […]
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What happens when assigning to the underscore pattern?
17 This is a question from Rust quiz 28: struct Guard; impl Drop for Guard { fn drop(&mut self) { print!("1"); } } fn main() { let _guard = Guard; print!("3"); let _ = Guard; print!("2"); } Such code prints 3121, in the third line of main, assigning to _ means a immediate drop. However, […]
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In C++ Inheritance, Derived class destructor not called when pointer object to base class is pointed to array of derived class
17 I have an Animal class with constructor and destructor. Cat have a private Brain* attribute. Upon construction, Cat creates his Brain using new Brain(); Upon destruction, Cat deletes his Brain. I don’t understand why The cat’s and brain’s destructors not called, when my Base class destructor is virtual? #include <iostream> using std::cout ; using […]
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How to Create a box with an angle one side and rounded corners via CSS?
11 So I currently find myself needing to make something like this. My first thought was to use clip-path, but the rounded corners would be hard to pull off, and it would be hard to maintain the 22.5 degrees when the button changes width because of its contents. So I ended up making each button […]
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Is every null pointer constant a null pointer?
9 From the C17 draft (6.3.2.3 ¶3): An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant.67) If a null pointer constant is converted to a pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal to a […]
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Unexpected uint64 behaviour 0xFFFF’FFFF’FFFF’FFFF – 1 = 0?
28 Consider the following brief numpy session showcasing uint64 data type import numpy as np a = np.zeros(1,np.uint64) a # array([0], dtype=uint64) a[0] -= 1 a # array([18446744073709551615], dtype=uint64) # this is 0xffff ffff ffff ffff, as expected a[0] -= 1 a # array([0], dtype=uint64) # what the heck? I’m utterly confused by this last […]
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“vagrant” will damage your computer. | macOS v12 (Monterey) #13132
17 Today morning suddenly I started getting this popup whenever I ran Vagrant up in my Mac. VirtualBox version 7.0.4 r154605 (Qt5.15.2). macOS v12 (Monterey), MacBook Pro (Retina, 15-inch, Mid 2015) Ubuntu LTS Settler Version Homestead Version Branch Status 20.04 11.x 12.x main Development/Unstable 20.04 11.x 12.x release Stable What’s wrong here? laravel laravel-5 laravel-8 homebrew […]