btr{wl} imm8, r/m[16|32] btr{wl} reg[16|32], r/m[16|32]
BIT[LeftSRC, RightSRC] -> CF
0 -> BIT[LeftSRC, RightSRC]
The value of the first operand (base) and the second operand (bit offset) are saved by btr into the carry flag and then it stores 0 in the bit.
btrl $253, 4(%edi) btrl $edx, 4(%edi)