Texas Instruments TMS320C64X manual DSPr4fft

DSP_r4fft

DSP_r4fft	Complex Forward FFT (radix 4)
		NOTE: This function is provided for backward compatibility with the C62x
		DSPLIB. It has not been optimized for the C64x architecture. You are advised
		to use one of the newly added FFT functions which have been optimized for the
		C64x.
Function		void DSP_r4fft (int nx, short * restrict x, const short * restrict w)
Arguments		nx	Number of complex elements in vector x. Must be a power of 4
			such that 4 ≤ nx ≤ 65536.
		x[2*nx]	Pointer to input and output sequences. Size 2*nx elements.
		w[nx]	Pointer to vector of FFT coefficients of size nx elements.
Description		This routine is used to compute FFT of a complex sequence size nx, a power
		of 4, with “decimation-in-frequency decomposition” method. The output is in
		digit-reversed order. Each complex value is with interleaved 16-bit real and
		imaginary parts.
Algorithm		This is the C equivalent of the assembly code without restrictions. Note that
		the assembly code is hand optimized and restrictions may apply.
		void DSP_r4fft (int nx, short x[ ], short w[ ])
	{

int	n1, n2, ie, ia1, ia2, ia3, i0, i1, i2, i3,
	j, k;
short	t, r1, r2, s1, s2, co1, co2, co3, si1,
	si2, si3;

n2 = nx; ie = 1;

for (k = nx; k > 1; k >>= 2) { n1 = n2;

n2 >>= 2; ia1 = 0;

for (j = 0; j < n2; j++) { ia2 = ia1 + ia1;

ia3 = ia2 + ia1;

co1 = w[ia1 * 2 + 1];

C64x+ DSPLIB Reference 4-95