void show_signed_high_prod(int x, int y)
{
printf("%d %d\n\n", x, y);
unsigned long long ullx = (unsigned long long)(unsigned)x;
unsigned long long ully = (unsigned long long)(unsigned)y;
unsigned long long ullxy = ullx*ully;
unsigned ullxy1 = ullxy>>32;
show_bytes(&ullx, 8);
show_bytes(&ully, 8);
show_bytes(&ullxy, 8);
show_bytes(&ullxy1, 4);
assert(ullxy1 == unsigned_high_prod(x, y));
printf("\n\n");
unsigned ullxy2 = unsigned_high_prod(x, y);
show_bytes(&ullxy2, 4);
signed long long sllx = (signed long long)x;
signed long long slly = (signed long long)y;
signed long long sllxy = sllx*slly;
signed long sllxy1 = sllxy >>32;
show_bytes(&sllx, 8);
show_bytes(&slly, 8);
show_bytes(&sllxy, 8);
show_bytes(&sllxy1, 4);
assert(sllxy1 == check_signed_high_prod(x, y));
printf("check_signed_high_prod = 0x%08X\n", check_signed_high_prod(x, y));
printf("\n");
assert(signed_high_prod(x,y) == check_signed_high_prod(x, y));
}
unsigned int unsigned_high_prod(unsigned x, unsigned y)
{
/* this solution is based on equation(2.18) on pp.90*/
int w = sizeof(int) << 3;
int msb_x = x >> (w-1);
int msb_y = y >> (w-1);
return signed_high_prod(x, y) + msb_y*x + msb_x*y;
}
unsigned unsigned_high_prod(unsigned x, unsigned y) {
unsigned p = (unsigned) signed_high_prod((int) x, (int) y);
/* Solution omitted */
return p;
}
