#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void writeInt(unsigned char* byteArray, unsigned long longInt, unsigned long int offset) {
	byteArray[offset+0] = (longInt >> 24) & 0xFF;
	byteArray[offset+1] = (longInt >> 16) & 0xFF;
	byteArray[offset+2] = (longInt >> 8) & 0XFF;
	byteArray[offset+3] = (longInt & 0XFF);
}

unsigned long int readInt(unsigned char* byteArray, unsigned long int offset) {
	unsigned long int result;

	result  = ((unsigned long int) byteArray[0+offset]) << 24;
	result |= ((unsigned long int) byteArray[1+offset]) << 16;
	result |= ((unsigned long int) byteArray[2+offset]) << 8;
	result |= ((unsigned long int) byteArray[3+offset]);

	return result;
}

int main(void)
{
	unsigned char *mem = NULL;
	unsigned long int size, i, x;
	unsigned int bsize = 1048576;
	int success = 1;

	size = 0;
	do
	{
		printf("Requested %i MB...", size);
		mem = malloc(size*bsize);
		if (mem)
		{
			for (i=0; i < (size*bsize)/4; i=i+4) {
				writeInt(mem,i,i*4);			
				//printf("write OK, ");
				
				x = readInt(mem,i*4);
				if (x==i) {
					//printf("read OK\n");
				} else {
					success=0;
					printf("read FAILED for index %i, value %i\n",i,x);
				}
			}
			if (1==success) {
				printf(" OK\n");
			} else {
				success=1;
				printf(" FAILED\n");
			}
			free(mem);

		}
		else
		{
			printf("Failed!\n");
		}
		size+=50;
	} while (NULL!=mem);
}

             total       used       free
Mem:         16073      16023         49
-/+ buffers/cache:      16016         56
Swap:        61035      58080       2954

Requested 70000 MB... OK
Requested 71000 MB... OK
Requested 72000 MB... OK
Requested 73000 MB... OK
Requested 74000 MB... OK
Requested 75000 MB...Failed!

$ free -m
             total       used       free
Mem:         16073        125      15947
-/+ buffers/cache:        114      15958
Swap:        61035         28      61006