Bit Test

The   x86 assembly language instruction stands for Bit Test and was added to the x86 instruction set with the 80386 processor. copies a bit from a given register to the carry flag.

Example: copy the third least significant bit from EAX to the carry flag

(Bit Test and Set) operates the same, but also sets the bit in the register, while  (Bit Test and Reset) resets it, and   (Bit Test and Complement) flips it.

Logical Explanation BT

BT SRC, POSITION

SRC Represent as bits array

POSITION Represent as numeric position From Right to Left Start at 0

CF     Carry Flag

Result CF = SRC[POSITION]

Logical Explanation BTC

BTC SRC, POSITION

SRC Represent as bits array for CF Result Represent as hex for SRC Result

POSITION Represent as numeric position From Right to Left Start at 0

CF     Carry Flag

Result CF = SRC[POSITION] XOR SRC, POW(2,POSITION)