用于迭代二维数组的嵌套循环的哪种排序更有效 [英] Which ordering of nested loops for iterating over a 2D array is more efficient

问题描述

以下哪种嵌套循环的顺序迭代二维数组在时间(缓存性能)方面更有效?为什么?

Which of the following orderings of nested loops to iterate over a 2D array is more efficient in terms of time (cache performance)? Why?

int a[100][100];

for(i=0; i<100; i++)
{
   for(j=0; j<100; j++)
   {
       a[i][j] = 10;    
   }
}

或

for(i=0; i<100; i++)
{
   for(j=0; j<100; j++)
   {
      a[j][i] = 10;    
   }
}

推荐答案

第一种方法稍微好一些，因为分配给的单元格彼此相邻.

The first method is slightly better, as the cells being assigned to lays next to each other.

第一种方法:

[ ][ ][ ][ ][ ] ....
^1st assignment
   ^2nd assignment
[ ][ ][ ][ ][ ] ....
^101st assignment

第二种方法:

[ ][ ][ ][ ][ ] ....
^1st assignment
   ^101st assignment
[ ][ ][ ][ ][ ] ....
^2nd assignment

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