Zfour1.cin

// zfour.cin is C++ implermentation of the routine required for compilation of examples with DCT .

#define SWAP(a,b) tempr=(a);(a)=(b);(b)=tempr
void zfour1(z_type data[], unsigned long nn, int isign)
{
unsigned long n,mmax,m,j,istep,i;
double wtemp,wr,wpr,wpi,wi,theta;
z_type tempr,tempi;
n=nn << 1;
j=1;
for(i=1;i<n;i+=2){
                       if(j>i){SWAP(data[j],data[i]);
                               SWAP(data[j+1],data[i+1]); }
                       m=n >> 1;
                       while (m >= 2 && j > m) { j -= m; m >>= 1; }
                       j += m;
                }
mmax=2;
while(n>mmax)
{ istep=mmax << 1;
  theta=isign*(6.28318530717959/mmax);
  wtemp=sin(0.5*theta);
  wpr = -2.0*wtemp*wtemp;
  wpi=sin(theta);
  wr=1.0;
  wi=0.0;
  for(m=1;m<mmax;m+=2)
       {for (i=m;i<=n;i+=istep)
          {j=i+mmax;
           tempr=wr*data[j]-wi*data[j+1];
           tempi=wr*data[j+1]+wi*data[j];
           data[j]=data[i]-tempr;
           data[j+1]=data[i+1]-tempi;
           data[i] += tempr;
           data[i+1] += tempi;
          }
        wr=(wtemp=wr)*wpr-wi*wpi+wr;
        wi=wi*wpr+wtemp*wpi+wi;
       }
  mmax=istep;
}
}
#undef SWAP

References

http://tori.ils.uec.ac.jp/TORI/index.php/Zfour1.cin