C++-为什么转置512×512矩阵，会比513×513矩阵慢很多？

Question

#define SAMPLES 1000
#define MATSIZE 512
 
#include <time.h>
#include <iostream>
int mat[MATSIZE][MATSIZE];
 
void transpose()
{
   for ( int i = 0 ; i < MATSIZE ; i++ )
   for ( int j = 0 ; j < MATSIZE ; j++ )
   {
       int aux = mat[i][j];
       mat[i][j] = mat[j][i];
       mat[j][i] = aux;
   }
}
 
int main()
{
   //initialize matrix
   for ( int i = 0 ; i < MATSIZE ; i++ )
   for ( int j = 0 ; j < MATSIZE ; j++ )
       mat[i][j] = i+j;
 
   int t = clock();
   for ( int i = 0 ; i < SAMPLES ; i++ )
       transpose();
   int elapsed = clock() - t;
 
   std::cout << "Average for a matrix of " << MATSIZE << ": " << elapsed / SAMPLES;
}

Answer 1

见过这个问题几次了，推荐你看下这个：

Why is transposing a matrix of 512x512 much slower than transposing a matrix of 513x513?

Answer 2

程序问题，你看看你那个什么，这样说吧，直接解决吧，你把define SAMPLES 1000中的1000改成514，看看时间差会不会短。
两者看似相差一个数，实则相差大概512*512时间哎。

Answer 3

elapsed / SAMPLES 整形除以整形 怎么可能得出小数来 ....
改成 elapsed / 1000.0