These instructions clear various flags. CLC clears the carry
flag; CLD clears the direction flag; CLI clears the
interrupt flag (thus disabling interrupts); and CLTS clears the
task-switched (TS) flag in CR0.
To set the carry, direction, or interrupt flags, use the STC,
STD and STI instructions (STC). To invert the carry
flag, use CMC (CMC).