gcc can use builtin functions in many cases, their documentation says: Many of these functions are only optimized in certain cases; if they are not optimized in a particular case, a call to the library function is emitted. so therefore gcc will not need to link against the math library when using the builtin function … 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.
The library that you are using needs to be placed after the files that use it when you are using it from the command line. So place -lm on after your C files on the command line. Reference
I have implemented Vecmathlib https://bitbucket.org/eschnett/vecmathlib/ as a generic libraries for two other projects (The Einstein Toolkit, and pocl http://pocl.sourceforge.net/). Vecmathlib is open source, and is written in C++.
No, and for good reason. In general, you’d need an infinite precision (and infinite time) to determine the exact mathematical result. Now most of the times you need only a few extra iterations to determine sufficient bits for rounding, but this number of extra bits depend on the exact result (simply put: when the result … Read more
The functions in stdlib.h and stdio.h have implementations in libc.so (or libc.a for static linking), which is linked into your executable by default (as if -lc were specified). GCC can be instructed to avoid this automatic link with the -nostdlib or -nodefaultlibs options. The math functions in math.h have implementations in libm.so (or libm.a for … Read more
You need to link with the math library (use a ‘-lm’ on the command line). In the constant case, the compiler is probably being smart and precomputing sqrt(2.0) (so the code that is compiled is essentially ‘b = 1.414…;’)
Take this code and put it in a file ceil.c: #include <math.h> #include <stdio.h> int main(void) { printf(“%f\n”, ceil(1.2)); return 0; } Compile it with: $ gcc -o ceil ceil.c $ gcc -o ceil ceil.c -lm One of those two should work. If neither works, show the complete error message for each compilation. Note that … Read more
When it works, it’s because the calculation was done by the compiler itself (and included in the binary as if you wrote it out) printf(“8\n”); When it doesn’t work, is because the pow function is included in the math library and the math library isn’t linked with your binary by default. To get the math … Read more
From school mathematics we know that the tangent has the definition tan(α) = sin(α) / cos(α) and we differentiate between four quadrants based on the angle that we supply to the functions. The sign of the sin, cos and tan have the following relationship (where we neglect the exact multiples of π/2): Quadrant Angle sin … Read more