Solution to the Project Euler problem #1 - For the multigrad blog (entry 6)

euler1_s6.c

/* To compile with: gcc euler1_s6.c -nostartfiles -s -O3 -o euler1_s6 */
/* How many 3, 5 and 15 are there in 999 (below 1000) */
#define QTY3 ( 999 / 3 )
#define QTY5 ( 999 / 5 )
#define QTY15 ( 999 / 15 )
/* Their sums */
#define SUM3 ( 3 * ( QTY3 * (QTY3 + 1) / 2 ) )
#define SUM5 ( 5 * ( QTY5 * (QTY5 + 1) / 2 ) )
#define SUM15 ( 15 * ( QTY15 * (QTY15 + 1) / 2 ) )
/* The answer */
#define RESULT ( SUM3 + SUM5 - SUM15 )

#include <stdio.h>

void _start(void) {
    printf("%u\n", RESULT);
    asm("movl $1,%eax;"
        "xorl %ebx,%ebx;"
        "int $0x80"
    );
}