SigLib FSk Function: SDA_FskModulate
The comment is mistaken.  The carrier frequency is 100 Hz.  The sample rate is 9600 Hz.  The carrier frequency divided by the sample rate is the carrier phase increment (phase change per sample), not the carrier frequency.  The units are radians / $2\pi$ (i.e. the phase increment is normalized from 0 to 1, not 0 to $2\pi$).  That phase increment can be used to index into a sine table to create a sinusoid.