Why does the order of the loops affect performance when iterating over a 2D array? [closed]
- by Mark
Possible Duplicate:
Which of these two for loops is more efficient in terms of time and cache performance
Below are two programs that are almost identical except that I switched the i and j variables around. They both run in different amounts of time. Could someone explain why this happens?
Version 1
#include <stdio.h>
#include <stdlib.h>
main () {
int i,j;
static int x[4000][4000];
for (i = 0; i < 4000; i++) {
for (j = 0; j < 4000; j++) {
x[j][i] = i + j; }
}
}
Version 2
#include <stdio.h>
#include <stdlib.h>
main () {
int i,j;
static int x[4000][4000];
for (j = 0; j < 4000; j++) {
for (i = 0; i < 4000; i++) {
x[j][i] = i + j; }
}
}
