Dspf_Sp_Cfftr2_Dit - Texas Instruments TMS320C67 DSP Series Programmer's Reference Manual

Benchmarks

DSPF_sp_cfftr2_dit

Function
Arguments
Description
-
Endianess: This code is endian neutral.
-
Interruptibility: This code is interrupt-tolerant but not interruptible.
Cycles (14*n/4 + 23)*log4(n) + 20
e.g., if n = 256, cycles = 3696.
Code size 1184
(in bytes)
Single-precision floating-point radix-2 FFT with complex input
void DSPF_sp_cfftr2_dit (float * x, float * w, short n)
x Pointer to complex data input.
w Pointer to complex twiddle factor in bit-reverse order.
Length of FFT in complex samples, power of 2 such that n ≥
n
32.
This routine performs the decimation-in-time (DIT) radix-2 FFT of the input
array x. x has N complex floating-point numbers arranged as successive real
and imaginary number pairs. Input array x contains N complex points (N*2 ele-
ments). The coefficients for the FFT are passed to the function in array w which
contains N/2 complex numbers (N elements) as successive real and imagi-
nary number pairs. The FFT coefficients w are in N/2 bit-reversed order The
elements of input array x are in normal order The assembly routine performs
4 output samples (2 real and 2 imaginary) for a pass through inner loop.
How to Use
void main(void)
{
gen_w_r2(w, N); // Generate coefficient table
bit_rev(w, N>>1); // Bit-reverse coefficient table
DSPF_sp_cfftr2_dit(x, w, N);
}
Note that (bit-reversed) coefficients for higher order FFT (1024 point) can be
used unchanged as coefficients for a lower order FFT (512, 256, 128 ... ,2) The
// input in normal order, output in
// order bit-reversed
// coefficient table in bit-reversed
// order
DSPLIB Reference
DSPF_sp_cfftr2_dit
4-13