mikeX - 2D pointers

/* * 2D arrays - pointer implementations */#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <sys/time.h>#include <time.h>typedef struct timeval tv;static inline doubletm(tv *start, tv *finish){	double tdiff, udiff, result;	if (!start || !finish) {		fprintf(stderr, "[tm] NULL pointer passed!\n");		exit(1);	}		tdiff = (double) (finish->tv_sec - start->tv_sec);	udiff = (double) (finish->tv_usec - start->tv_usec);		result = tdiff + udiff / 1000000000;	return result;}static inline voidprintt(tv *start, tv *finish, const char *msg){	printf("%s %.5f seconds\n", msg, tm(start, finish));}int main (int argc, char **argv){	double **a, **b;	long rows = 1024, cols = 1024, i, j;	tv *beg = NULL, *end = NULL;	beg = (tv*) malloc(sizeof(tv));	end = (tv*) malloc(sizeof(tv));		if (argc > 1) {		rows = strtol(argv[1], NULL, 10);		if (argc > 2)			cols = strtol(argv[2], NULL, 10);	}	/* continuous allocation */	a = (double**) malloc(rows * sizeof(double*) + rows * cols * sizeof(double));		for (i = 0; i < rows; i++)		a[i] = &a[rows + i*cols];		/* non-continuous allocation */	b = (double**) malloc(i * sizeof(double*));	for (i = 0; i < rows; i++)		b[i] = (double*) malloc(cols * sizeof(double));		/* speed tests */	gettimeofday(beg, NULL);	for (i = 0; i < rows; i++)		for (j = 0; j < cols; j++)			a[i][j] = 1.0;	gettimeofday(end, NULL);	printt(beg, end, "a init");	gettimeofday(beg, NULL);	for (i = 0; i < rows; i++)		for (j = 0; j < cols; j++)			b[i][j] = 1.0;	gettimeofday(end, NULL);	printt(beg, end, "b init");	free(beg);	free(end);	return 0;}