图1 卷积计算界面

1.1 主程序代码(省略了部分不关键代码)

void CInterVolveDlg::CalTheNumByArray() { this->UpdateData(TRUE);
FFuncs funcs[2] = {funch1,funch2};
int n = this->m_ValueN; double* x = new double[2*(n+1)];
//x(n) double* y = new double[2*(n+1)];
//y(n) double* h = new double[2*(n+1)];
//h(n)
//1.init x(n),h(n),y(n) CButton* pbtn = (CButton*) this->GetDlgItem(IDC_RADIO1);
int nChoseItem = 0;
//函数选择 if(pbtn->GetCheck()) { nChoseItem = 0; } e
lse { nChoseItem = 1; } for(int i= 0;i<2*(n+1);i++) { if(i< n+1) { x[i] = 1; h[i] = funcs[nChoseItem](i); }
else { x[i] = 0; h[i] = 0; } }
//2.y(i)=SUM(x(m)*h(i-m)) m=0..i for(i=0;i<2*(n+1);i++) { y[i] = Calcy(x,h,i); }
//显示结果 delete[] x; delete[] y; delete[] h;}

1.2 各个子函数实现

typedef double (* FFuncs)(int);
//h1(x) doublefunch1(intn) { doublefbase = (double)4/(double)5; double fr = std::pow(fbase, n); return fr; }
//h2(x)doublefunch2(intn) { doublefpi = 3.1415927; return 0.5*sin((double)0.5*n); }
//y(n)//y(n)=sum(x(m)*y(n-m))m=0..n doubleCalcy(double x[],double h[],int n) {double yvalue = 0;
for(int m= 0;m<=n;m++) { yvalue += x[m]*h[n-m]; }
return yvalue;}

2、DFT与FFT实现

程序界面,具体实现见注释及代码:

图2 DFT与FFT实现界面

2.1 主程序代码

void CFFTConversionDlg::OnBnClickedBtncal() { this->UpdateData(TRUE);
int nN = this->m_NumN;
float fF = this->m_NumF;
float fT = this->m_NumT;
bool bIsTimesof2 = false;
for(int i= 0;i<100;i++) { if(nN==(2 < < i)) { bIsTimesof2 = true; break; } }
if(!bIsTimesof2) { AfxMessageBox("N请输入一个以2为底的幂级数!");
this->GetDlgItem(IDC_EDTN)->SetFocus();
return; } COMP* x = new COMP[nN];
//x(n) COMP* X = new COMP[nN];//X(k) initX(nN,x,fF,fT);
CButton* pRadio = (CButton*)this->GetDlgItem(IDC_RADIODFT);
if(pRadio->GetCheck()) { DFT(nN,x,X); }
else { FFT(nN,x,X); }
char buffer[256];
COMP source = X[nN-1];
sprintf(buffer,"%f+%fi",source.real(),source.imag());
CWnd* pwnd = this->GetDlgItem(IDC_EDTRET);
pwnd->SetWindowText(buffer);
CListCtrl* pList=(CListCtrl*) this->GetDlgItem(IDC_LIST1);
CListOper oper;
oper.FillList(*pList,nN,x,X);
delete[] x;
delete[] X;}

2.2 子函数代码

说明:其中COMP为复数类型

/*******************************************
Name :DFT* Function
:Disperse Fuliye Transformation* Params
:N -- Total count of sampling points* X -- Input sequence* Return
:XN(k)=sum[x(n)*Pow(e,j2*Pi/N)]
* k,n
:0..N-1
*******************************************
/void DFT(int N,COMP x[],COMP XK[]){ double C = (2*pi)/N;
COMP t(0,0),ret(0,0);
for(int k=0;k < N;k++)
{ ret = COMP(0,0);
for(int i=0;i< N;i++) { t = COMP(cos(C*k*i),-sin(C*k*i));
ret += x[i]*t; } XK[k] = ret; } }/
*******************************************
Name
:FFT* Function
:Fast Fuliye Transformation* Params
:N -- Total count of sampling points* X -- Input sequence* Return
:XN(k)=sum[x(n)*Pow(e,j2*Pi/N)] * k,n
:0..N-1
*******************************************
/void FFT(int N,COMP X[],COMP XK[]){ int j=0; COMP U=0,W=0;
COMP* A = XK;
//Adjust sequence for(int i=0;i< N;i++) { if(i==0) { A[0] = X[0]; }
else { j=GetInverse(N,j);
A[i] = X[j]; } }
//确定级别数
for(int M=0;M< N;M++) { if((1<< M)==N) break; }
for(int L=1;L<=M;L++)//1-M级依次确定 { int LE = (int)pow(2,L);
//间隔 int LE1 = LE/2;
//W级数,如W0,W1,W2... W=COMP(cos(pi/LE1),-sin(pi/LE1));
U=COMP(1,0); for(j=0;j< LE1;j++)
// { i=j; while(i< N) { int IP = i+LE1; COMP T=A[IP]*U;
A[IP]=A[i]-T;//蝶形计算 A[i]=A[i]+T; i+=LE; } U=U*W;
//不同的W次幂 } }}void initX(int N,COMP x[],float F,float T){
for(int i=0;i< N;i++) { x[i] = COMP(cos(2*pi*F*T*i),0);
}}

3.2 子函数代码实现

/*********************************************************************
Name :
FuncHd* Function:
Hd()--RequIRed frequency response function
***********************************************************************
/COMP FuncHd(double LowLimit,double UpperLimit,COMP x){
if(x.real()>UpperLimit||x.real() < LowLimit) return 0;
else return 1;
}void FIR(double LowLimit,double UpperLimit,int N,COMP Hn[])
{ int M = 2*N;
for(int i=0;i < N;i++) { Hn[i] = COMP(0,0);
for(int k=0;k < M;k++) { COMP C = COMP(cos(2*pi*i*k/(double)M),sin(2*pi*i*k/(double)M));
Hn[i] += C*FuncHd(LowLimit,UpperLimit,COMP(cos(2*pi*k/(double)M),sin(2*pi*k/(double)M)));
} Hn[i] = Hn[i]*COMP(1/(double)M,0);
}}

4、结束语

　　虽然现在DSP算法都有很好C语言实现。但是能够通过自己动手编写代码加深对基础知识的掌握，对自己进行数据采集器件的控制还是有很多益处的。