static void rdft_calc_c(RDFTContext *s, FFTSample *data) { int i, i1, i2; FFTComplex ev, od; const int n = 1 << s->nbits; const float k1 = 0.5; const float k2 = 0.5 - s->inverse; const FFTSample *tcos = s->tcos; const FFTSample *tsin = s->tsin; if (!s->inverse) { s->fft.fft_permute(&s->fft, (FFTComplex*)data); s->fft.fft_calc(&s->fft, (FFTComplex*)data); } /* i=0 is a special case because of packing, the DC term is real, so we are going to throw the N/2 term (also real) in with it. */ ev.re = data[0]; data[0] = ev.re+data[1]; data[1] = ev.re-data[1]; for (i = 1; i < (n>>2); i++) { i1 = 2*i; i2 = n-i1; /* Separate even and odd FFTs */ ev.re = k1*(data[i1 ]+data[i2 ]); od.im = -k2*(data[i1 ]-data[i2 ]); ev.im = k1*(data[i1+1]-data[i2+1]); od.re = k2*(data[i1+1]+data[i2+1]); /* Apply twiddle factors to the odd FFT and add to the even FFT */ data[i1 ] = ev.re + od.re*tcos[i] - od.im*tsin[i]; data[i1+1] = ev.im + od.im*tcos[i] + od.re*tsin[i]; data[i2 ] = ev.re - od.re*tcos[i] + od.im*tsin[i]; data[i2+1] = -ev.im + od.im*tcos[i] + od.re*tsin[i]; } data[2*i+1]=s->sign_convention*data[2*i+1]; if (s->inverse) { data[0] *= k1; data[1] *= k1; s->fft.fft_permute(&s->fft, (FFTComplex*)data); s->fft.fft_calc(&s->fft, (FFTComplex*)data); } }