In C++, std::abs is overloaded for both signed integer and floating point types. std::fabs only deals with floating point types (pre C++11). Note that the std:: is important; the C function ::abs that is commonly available for legacy reasons will only handle int! The problem with float f2= fabs(-9); is not that there is no … Read more
pow() works with real floating-point numbers and uses under the hood the formula pow(x,y) = e^(y log(x)) to calculate x^y. The int are converted to double before calling pow. (log is the natural logarithm, e-based) x^2 using pow() is therefore slower than x*x. Edit based on relevant comments Using pow even with integer exponents may … Read more
You can use (n & 1) instead of n % 2 and << 1 instead of * 2 if you want to be super-pedantic, er I mean optimized. So the fastest way to compute in an 8086 processor is: 1 – ((n & 1) << 1) I just want to clarify where this answer is … Read more
The header <math.h> is a C std lib header. It defines a lot of stuff in the global namespace. The header <cmath> is the C++ version of that header. It defines essentially the same stuff in namespace std. (There are some differences, like that the C++ version comes with overloads of some functions, but that … Read more
Actually, because of old and annoying legacy, almost none of the math functions can be constexpr, since they all have the side-effect of setting errno on various error conditions, usually domain errors.
The LL makes the integer literal of type long long. So 2LL, is a 2 of type long long. Without the LL, the literal would only be of type int. This matters when you’re doing stuff like this: 1 << 40 1LL << 40 With just the literal 1, (assuming int to be 32-bits, you … Read more
In C++, it’s always sufficient to use std::abs; it’s overloaded for all the numerical types. In C, abs only works on integers, and you need fabs for floating point values. These are available in C++ (along with all of the C library), but there’s no need to use them.