ibit_reversal_intr.c

用dsp解压mp3程序的算法

/************************************************************************
*   ibit_reversal_intr.c- Arrange input samples in bit-reverse 
*                         addressing order using C5000 intrinsics for CCS 
*                         The index j is the bit reverse of i 
*
************************************************************************/

#include "def_complex_fixpt.h"  /* integer complex.h header file */

void ibit_reversal_intr(complex *X, unsigned int EXP)
{
    unsigned int i,j,k;
    unsigned int N=1<<EXP;     /* Number of points for FFT */
    unsigned int N2=N>>1;
    complex temp;              /* temporary storage of int complex variable */	
	
    for (j=0,i=1;i<N-1;i++)
    {
        k=N2;
        while(k<=j)
        {
            j-=k;
            k>>=1;
        }
        j+=k;

        if (i<j)
        {
            temp = X[j];
            X[j] = X[i];
            X[i] = temp;
        }
    }  
}