提高C循环的效率 [英] Improving efficiency of a C loop

问题描述

我有一些可以提高效率的有效C代码.我知道最好避免语句循环，但是我在这里努力解决这个问题.谁能建议我如何使以下代码更有效?

I have some working c code that I am looking to make more efficient. I know that it is best to avoid if statements in loops however I am struggling to get around this here. Can anyone suggest how I could make the following code more efficient?

for(iy=0;iy<Ny;iy++) {
for(ix=0;ix<Nx;ix++) {


    if (ix==0) {
      pudx = (u[1][iy] + u[Nx-1][iy] - 2.0*u[0][iy])/(calc1);   
    } else if (ix==Nx-1) {
      pudx = (u[0][iy] + u[Nx-2][iy] - 2.0*u[Nx-1][iy])/(calc1);  
    } else {
      pudx = (u[ix+1][iy] + u[ix-1][iy] - 2.0*u[ix][iy])/(calc1);
    }

    if (iy==0) {
      pudy = (u[ix][1] + u[ix][Ny-1] - 2.0*u[ix][0])/(calc2);    
    } else if (iy==Ny-1) {
      pudy = (u[ix][0] + u[ix][Ny-2] - 2.0*u[ix][Ny-1])/(calc2);   
    } else {
      pudy = (u[ix][iy+1] + u[ix][iy-1] - 2.0*u[ix][iy])/(calc2);
    }


    u_new[ix][iy] = 2.0*u[ix][iy] - u_old[ix][iy] + calc*(pudx+pudy);

  }
}

我知道可以使用编译器来完成这种优化，但是我想通过-o标志(不进行编译器优化)来提高效率.

I am aware that such optimization can be done with a compiler but I would like to improve the efficiency with the -o flag (no compiler optimization).

推荐答案

在@JohnBollinger之后:(显然是未经测试的)

After @JohnBollinger: (untested, obviously)

unsigned ix, iy;
for(iy=0;iy<Ny;iy++) {
  unsigned  yl,yh;

  yl = (iy -1) %Ny; yh = (iy +1) %Ny;
  for(ix=0;ix<Nx;ix++) {
      unsigned xl,xh;

      xl = (ix -1) %Nx; xh = (ix +1) %Nx;
      yl = (iy -1) %Ny; yh = (iy +1) %Ny;

      pudx = (u[xh][iy] + u[xh][iy] - 2.0*u[ix][iy])/(calc1);   
      pudy = (u[ix][yh] + u[ix][yl] - 2.0*u[ix][iy])/(calc2);    

    u_new[ix][iy] = 2.0*u[ix][iy] - u_old[ix][iy] + calc*(pudx+pudy);

  }
}

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