Thread: help undestanding what pointer is being passed

Hello,

I am refactoring some code that uses a non-GPL'ed FFT function (will replace with fftw), but I don't yet understand what exactly is being passed. Specifically, I don't understand what is pointed to when you pass "*pointer -1", as shown below:

My fft buffer is allocated with:
pFFftBuffer = (float *) calloc(sizeFft+1, sizeof(float));

and then passed to the fft function with:
realft (pFFftBuffer-1, sizeMag, -1);

realft is defined as:
void realft(float *data, int n, int isign);

If anyone could help me understand what data realft is receiving, I would be deeply thankful.

regards,
Rich