Yolov3源码解析：reorg_cpu

素颜马尾好姑娘i 2022-05-09 03:58 178阅读 0赞

函数原型如下，

void reorg_cpu(float *x, int out_w, int out_h, int out_c, int batch, int stride, int forward, float *out)
    {
        int b,i,j,k;
        int in_c = out_c/(stride*stride); 
    
        //printf("\n out_c = %d, out_w = %d, out_h = %d, stride = %d, forward = %d \n", out_c, out_w, out_h, stride, forward);
        //printf("  in_c = %d,  in_w = %d,  in_h = %d \n", in_c, out_w*stride, out_h*stride);
    
        for(b = 0; b < batch; ++b){
            for(k = 0; k < out_c; ++k){
                for(j = 0; j < out_h; ++j){
                    for(i = 0; i < out_w; ++i){
                        int in_index  = i + out_w*(j + out_h*(k + out_c*b));
                        int c2 = k % in_c;     // 分成4个后属于哪个,求具体位置，e.g. 125%64 = 61
                        int offset = k / in_c; // 分成4个后属于哪个 e.g. 125/64=1
                        int w2 = i*stride + offset % stride; 
                        int h2 = j*stride + offset / stride;
                        int out_index = w2 + out_w*stride*(h2 + out_h*stride*(c2 + in_c*b));
                        if(forward) out[out_index] = x[in_index];    // used by default for forward (i.e. forward = 0)
                        else out[in_index] = x[out_index];
                    }
                }
            }
        }
    }

考虑 ! forward 的情况，相当于一个大channel拆分成stride\*stride个子channel  
考虑  forward 的情况，相当于stride\*stride个子channel合成一个大channel  
例如stride=2时，每个子channel中矩阵的大小为8\*8＝64，则大channel矩阵的大小为16\*16＝256

输入矩阵为8x256x8x8：  
in\_index = i(col) + width\*j(row) + width\*heigth\*c + width\*hight\*out\_channel\*b  
表示：第b个batch, 第c个channel, 第j个行, 第i个列,

输出矩阵为8x64x16x16：（注意此矩阵宽为width\*stride, 高为height\*stride）  
out\_index = w2 + width\*stride\*h2 + width\*stride\*height\*stride\*c2 + width\*stride\*height\*stride\*in\_channel\*b  
表示：第b个batch, 第c2个channel, 第h2个行, 第w2个列,

根据源码中的计算，举个例子，如图，  
![70][]

k = channel = 5  
\-> i j k b = 3,4,5,6 ==> c2 = k%64 = 5 offset = 5/64=0 w2 = 6 h2 = 8  
\-> i j k b = 3,5,5,6 ==> c2 = k%64 = 5 offset = 5/64=0 w2 = 6 h2 = 10  
\-> i j k b = 4,4,5,6 ==> c2 = k%64 = 5 offset = 5/64=0 w2 = 8 h2 = 8  
\-> i j k b = 4,5,5,6 ==> c2 = k%64 = 5 offset = 5/64=0 w2 = 8 h2 = 10

k = chanel = 64+5 = 69  
\-> i j k b = 3,4,68,6 ==> c2 = k%64 = 5 offset = 69/64=1 w2 = 7 h2 = 8  
\-> i j k b = 3,5,68,6 ==> c2 = k%64 = 5 offset = 69/64=1 w2 = 7 h2 = 10  
\-> i j k b = 4,4,68,6 ==> c2 = k%64 = 5 offset = 69/64=1 w2 = 9 h2 = 8  
\-> i j k b = 4,5,68,6 ==> c2 = k%64 = 5 offset = 69/64=1 w2 = 9 h2 = 10

k = chanel = 64 + 64 + 5 = 133  
\-> i j k b = 3,4,68,6 ==> c2 = k%64 = 5 offset = 133/64=2 w2 = 6 h2 = 9  
\-> i j k b = 3,5,68,6 ==> c2 = k%64 = 5 offset = 133/64=2 w2 = 6 h2 = 11  
\-> i j k b = 4,4,68,6 ==> c2 = k%64 = 5 offset = 133/64=2 w2 = 8 h2 = 9  
\-> i j k b = 4,5,68,6 ==> c2 = k%64 = 5 offset = 133/64=2 w2 = 8 h2 = 11

k = chanel = 64 + 64 + 64 + 5 = 192+5 = 197  
\-> i j k b = 3,4,68,6 ==> c2 = k%64 = 5 offset = 197/64=3 w2 = 7 h2 = 9  
\-> i j k b = 3,5,68,6 ==> c2 = k%64 = 5 offset = 197/64=3 w2 = 7 h2 = 11  
\-> i j k b = 4,4,68,6 ==> c2 = k%64 = 5 offset = 197/64=3 w2 = 9 h2 = 9  
\-> i j k b = 4,5,68,6 ==> c2 = k%64 = 5 offset = 197/64=3 w2 = 9 h2 = 11

[70]: /images/20220509/a7afd9ddcef048bb9757d90b92014e7b.png