#include <stdio.h>
 
int main(void)
{
	int rows = 3, cols = 3;
	int x, y;
 
	printf("Suppose we have the following bitmap with (x, y) coordinates\n");
	printf("where x is the column (HORIZONTAL coordinate)\n");
	printf("and y is the row (VERTICAL coordinate)\n");
	printf("\n");
	printf("(0, 0)  (1, 0)  (2, 0)\n");
	printf("(0, 1)  (1, 1)  (2, 1)\n");
	printf("(0, 2)  (1, 2)  (2, 2)\n");
	printf("\n");
	printf("If it is stored in row-major order, then the pixels go from\n");
	printf("left to right, top to bottom in memory, in this order:\n");
	printf("  \n");
	printf("(0, 0) (1, 0) (2, 0) (0, 1) (1, 1) (2, 1) (0, 2) (1, 2) (2, 2)    [ROW MAJOR]\n");
	printf("\n");
	printf("If it is stored in column-major order, then the order is:\n");
	printf("  \n");
	printf("(0, 0) (0, 1) (0, 2) (1, 0) (1, 1) (1, 2) (2, 0) (2, 1) (2, 2)    [COLUMN MAJOR]\n");
	printf("\n");
	printf("Now let's try it!\n\n");
 
	printf("Outer loop = rows, Inner loop = columns:\n\n");
	for (x = 0; x < rows; ++x) // <-- outer
		for (y = 0; y < cols; ++y) // <-- inner
			printf("(%d, %d) ", x, y);
 
	printf("\n\n= COLUMN-MAJOR\n\n");
	printf("----\n\n");
 
	printf("Outer loop = columns, Inner loop = rows:\n\n");
	for (y = 0; y < cols; ++y) // <-- outer
		for (x = 0; x < rows; ++x) // <-- inner
			printf("(%d, %d) ", x, y);
 
	printf("\n\n= ROW-MAJOR\n\n");
 
	printf("Therefore the order which best matches the layout of the pixels\n");
	printf("in memory (and hence performance due to better cache coherency)\n");
	printf("is:\n");
	printf("  Outer loop: columns\n");
	printf("  Inner loop: rows\n");
 
	return 0;
}
 

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