cfft_simd.c

在ADSP-2126x上编写的优化过的FFT程序（用c和汇编编写）。

/*******************************************************************************
*
* Function:  cfft_simd_twiddle_calc - Calculate cfft_simd twiddle factors
*
* Synopsis:  #include "cfft_simd.h"
*            
*
*
// prototype		
//==================================================================================
//void cfft_simd_twiddle_calc(Tcfft_simd pm *pfft);	// pointer to fft object
//
//==================================================================================
* Description:  
*				This function calculates twiddle factors that are used by the cfft_simd
*				routine.  Two arrays are filled pfft->twid_real and pfft->twid_imag.
*				pfft->N/2 factors for each array are calculated according to the 
*				following equations:
*					pfft->twid_real[k] = cos(2*pi/pfft->N*k);
*					pfft->twid_real[k] = -sin(2*pi/pfft->N*k); // k=0:N/2-1
* Caution:
*				The function cfft_simd_init must be called before calling this function.
*				Other wise this function will not have a valid pointer to the arrays
*				where the twiddle factors are stored.
*
* Author:	Darrel Judd
*				Judd Labs, Inc.
*				801-756-2057
*				[e-mail]
*
* Revisions:
*				Created June, 2003 - Darrel Judd
************************************************************************************/



#include "cfft_simd.h"
#define pi (3.141592654)
void cosf_sinf_simd(float *x,float *y);
void cfft_simd_twiddle_calc(Tcfft_simd pm *pfft)	// pointer to fft object
{
	U32 i;
	float x[2];		// inputs to cosf_sinf_simd routine
	float y[2];		// outputs to cosf_sinf_simd routine
	float c = 2*pi/(float) pfft->N;
	float k;
	
	// calculate twiddle factors
#pragma SIMD_for	
	for(i=0;i<pfft->N/2;i++)
	{
		k=(float) i;
		// 2*pi/N * k :k=0-N/2-1
		x[0]=k*c;
		x[1]=-k*c;
		// calculate cosine and sine in parallel
		cosf_sinf_simd(x,y);
		// store results
		pfft->twid_real[i]=y[0];
		pfft->twid_imag[i]=y[1];
	}
}