fmod() computes the floating-point remainder of x modulo y.
    It returns the remainder r = x-n*y, where n = trunc(x/y). The
    remainder is computed exactly.

    The result has the same sign as x and a magnitude less than the
    magnitude of y.

                           Entry-Point Names

    Generic                               Compaq
    Function   Data Type   OpenVMS        Tru64 UNIX
    Name       Required    Alpha          Alpha

    fmod       S_FLOAT     math$mod_s     fmodf
               T_FLOAT     math$mod_t     fmod
               X_FLOAT     math$mod_x     fmodl
               F_FLOAT     math$mod_f
               G_FLOAT     math$mod_g