remainder() returns the remainder r = x-n*y, where n = rint(x/y).
    Additionally, if |n-x/y| = 1/2, then n is even. Consequently, the
    remainder is computed exactly, and |r| is less than or equal to
    |y|/2. The drem() and remainder()  functions are aliases of each
    other.

                           Entry-Point Names

    Generic
    Function   Data Type   OpenVMS                Tru64 UNIX
    Name       Required

    remainder  S_FLOAT     math$rem_s             remainderf
               T_FLOAT     math$rem_t             remainder
               X_FLOAT     math$rem_x             remainderl
               F_FLOAT     math$rem_f
               G_FLOAT     math$rem_g