Bit Test

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The BT x86 assembly language instruction stands for Bit Test and was added to the x86 instruction set with the 80386 processor. BT copies a bit from a given register to the carry flag.[1]

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


BTS (Bit Test and Set) operates the same, but also sets the bit in the register,[2] while BTR (Bit Test and Reset) resets it,[3] and BTC (Bit Test and Complement) flips it.[4]


  1. ^ "BT - Bit Test". Retrieved 2011-08-21. 
  2. ^ "BTS - Bit Test and Set". Retrieved 2011-08-21. 
  3. ^ "BTR - Bit Test and Reset". Retrieved 2011-08-21. 
  4. ^ "BTC -- Bit Test and Complement". Retrieved 2012-11-04.