c6x: digitrev for complex values

Hi,

I got this function of TI's site for the c6711 -

void digitrev(int *x, unsigned int *index, int n, int radix)
{
	int i,j,a,b;
	int xi, xj;
	int nbits, nbot, ntop, ndiff, n2, astep, radN;
	
	/* short leftzeros; */
	int *xs = (int *) x;
	
	nbits = 0;
	i = n;
	while (i > 1)
	{
	i = i >> 1;
	nbits++;
	}

	radN = 0;
	i = radix;
	while (i > 1)
	{
		i = i >> 1;
		radN++;
	}
	nbot = nbits / (2*radN);
	nbot = nbot * radN;
	ndiff = nbits % (2*radN);
	ntop = nbot + ndiff;
	n2 = 1 << ntop;
	astep = 1 << ndiff;
	for (a = 0, i = 0; a < n2; a += astep)
	{
		for (b = 0; b < n2; b++, i++) 
		{
			j = (index[b] << nbot) + index[a];
			if (i < j) 
			{
				xi = x[i];
				xj = x[j];
				x[i] = xj;
				x[j] = xi;
			}
		}
	}
}

I'm looking for optimized code for swapping complex values from the
function DSPF_sp_cfftr4_dif, not plain old ints as above. What I'm
having to do at the moment is -

DSPF_sp_cfftr4_dif(FFTBuffer, PSD_W, FFT_SIZE);
	
digitrev_index(PSD_Indeces, FFT_SIZE, 4);
	
for (i = 0,j=0; i < FFT_SIZE; i++,j+=2) 
{
  FFTBuffer2[j] = FFTBuffer[PSD_Indeces[i]*2];
  FFTBuffer2[j+1] = FFTBuffer[PSD_Indeces[i]*2+1];
}

CalcFFTMag(FFTBuffer2,FFT_SIZE,FFT_mag);  

My code for digitrev_index is -

void digitrev_index(unsigned int *index, int n2, int radix)
{
	int i,j,k;
	index[0] = 0;
	for ( i = 1, j = n2/radix + 1; i < n2 - 1; i++)
	{
		index[i] = j - 1;
		for (k = n2/radix; k*(radix-1) < j; k /= radix)
			j -= k*(radix-1);
		j += k;
	}
	index[n2 - 1] = n2 - 1;
}

Maybe theres an optimized version of this also?

Thanks for your help,

Barry.

Hi, 

I'm sure some of you guys have have used DSPF_sp_cfftr4_dif before.
What code did you use to sort out the output array?

Thanks,

Barry.



bg_ie@yahoo.com (Barry) wrote in message news:<731cea69.0309231158.1b40e19a@posting.google.com>...
> Hi,
> 
> I got this function of TI's site for the c6711 -
> 
> void digitrev(int *x, unsigned int *index, int n, int radix)
> {
> 	int i,j,a,b;
> 	int xi, xj;
> 	int nbits, nbot, ntop, ndiff, n2, astep, radN;
> 	
> 	/* short leftzeros; */
> 	int *xs = (int *) x;
> 	
> 	nbits = 0;
> 	i = n;
> 	while (i > 1)
> 	{
> 	i = i >> 1;
> 	nbits++;
> 	}
> 
> 	radN = 0;
> 	i = radix;
> 	while (i > 1)
> 	{
> 		i = i >> 1;
> 		radN++;
> 	}
> 	nbot = nbits / (2*radN);
> 	nbot = nbot * radN;
> 	ndiff = nbits % (2*radN);
> 	ntop = nbot + ndiff;
> 	n2 = 1 << ntop;
> 	astep = 1 << ndiff;
> 	for (a = 0, i = 0; a < n2; a += astep)
> 	{
> 		for (b = 0; b < n2; b++, i++) 
> 		{
> 			j = (index[b] << nbot) + index[a];
> 			if (i < j) 
> 			{
> 				xi = x[i];
> 				xj = x[j];
> 				x[i] = xj;
> 				x[j] = xi;
> 			}
> 		}
> 	}
> }
> 
> I'm looking for optimized code for swapping complex values from the
> function DSPF_sp_cfftr4_dif, not plain old ints as above. What I'm
> having to do at the moment is -
> 
> DSPF_sp_cfftr4_dif(FFTBuffer, PSD_W, FFT_SIZE);
> 	
> digitrev_index(PSD_Indeces, FFT_SIZE, 4);
> 	
> for (i = 0,j=0; i < FFT_SIZE; i++,j+=2) 
> {
>   FFTBuffer2[j] = FFTBuffer[PSD_Indeces[i]*2];
>   FFTBuffer2[j+1] = FFTBuffer[PSD_Indeces[i]*2+1];
> }
> 
> CalcFFTMag(FFTBuffer2,FFT_SIZE,FFT_mag);  
> 
> My code for digitrev_index is -
> 
> void digitrev_index(unsigned int *index, int n2, int radix)
> {
> 	int i,j,k;
> 	index[0] = 0;
> 	for ( i = 1, j = n2/radix + 1; i < n2 - 1; i++)
> 	{
> 		index[i] = j - 1;
> 		for (k = n2/radix; k*(radix-1) < j; k /= radix)
> 			j -= k*(radix-1);
> 		j += k;
> 	}
>  index[n2 - 1] = n2 - 1;
> }
> 
> Maybe theres an optimized version of this also?
> 
> Thanks for your help,
> 
> Barry.