Major bugfix and minor bugfix

main.c

 
 			case 0xC000: // random generator
 				reg = (opcode & 0x0F00) >> 8;
-				state.registers[reg] = (rand() % 255) & ((byte) opcode);
+				state.registers[reg] = (rand() % 256) & ((byte) opcode);
 				if (DEBUG) printf("Storing random in %i (%x)\n", reg, state.registers[reg]);
 
 				break;
 
 			case 0xD000: // draw sprite
+				state.registers[0xF] = 0;
+
 				first = (opcode & 0x0F00) >> 8;
 				second = (opcode & 0x00F0) >> 4;