FMOD(3) Library Functions Manual FMOD(3)

fmod, fmodf, fmodl
floating-point remainder functions

library “libm”

#include <math.h>
fmod(double x, double y);
fmodf(float x, float y);
long double
fmodl(long double x, long double y);

As usual, the Mdocdate mechanism is not used for the Dd macro on FreeBSD.
There is an additional LIBRARY section between NAME and SYNOPSIS, containing the Lb macro with the argument ‘libm’. That is rendered as
Math Library (libm, -lm)
on FreeBSD and as
library ``libm''
on OpenBSD.
June 19, 2008