extern void abort (); extern int abs (int __x) __attribute__ ((__nothrow__, __leaf__)) __attribute__ ((__const__)); static int foo (unsigned char *w, int i, unsigned char *x, int j) { int tot = 0; for (int a = 0; a < 16; a++) { for (int b = 0; b < 16; b++) tot += abs (w[b] - x[b]); w += i; x += j; } return tot; } void bar (unsigned char *w, unsigned char *x, int i, int *result) { *result = foo (w, 16, x, i); } int main (void) { unsigned char m[256]; unsigned char n[256]; int sum, i; for (i = 0; i < 256; ++i) if (i % 2 == 0) { m[i] = (i % 8) * 2 + 1; n[i] = -(i % 8); } else { m[i] = -((i % 8) * 2 + 2); n[i] = -((i % 8) >> 1); } bar (m, n, 16, &sum); if (sum != 32384) abort (); return 0; }