GNU Info

(nasm.info)Section B.4.17

---

Next: Section B.4.18 Prev: Section B.4.16 Up: Section B.4

---

Enter node , (file) or (file)node

B.4.17. `BT', `BTC', `BTR', `BTS': Bit Test
-------------------------------------------

     BT r/m16,reg16                ; o16 0F A3 /r         [386]
     BT r/m32,reg32                ; o32 0F A3 /r         [386]
     BT r/m16,imm8                 ; o16 0F BA /4 ib      [386]
     BT r/m32,imm8                 ; o32 0F BA /4 ib      [386]

     BTC r/m16,reg16               ; o16 0F BB /r         [386]
     BTC r/m32,reg32               ; o32 0F BB /r         [386]
     BTC r/m16,imm8                ; o16 0F BA /7 ib      [386]
     BTC r/m32,imm8                ; o32 0F BA /7 ib      [386]

     BTR r/m16,reg16               ; o16 0F B3 /r         [386]
     BTR r/m32,reg32               ; o32 0F B3 /r         [386]
     BTR r/m16,imm8                ; o16 0F BA /6 ib      [386]
     BTR r/m32,imm8                ; o32 0F BA /6 ib      [386]

     BTS r/m16,reg16               ; o16 0F AB /r         [386]
     BTS r/m32,reg32               ; o32 0F AB /r         [386]
     BTS r/m16,imm                 ; o16 0F BA /5 ib      [386]
     BTS r/m32,imm                 ; o32 0F BA /5 ib      [386]

   These instructions all test one bit of their first operand, whose
index is given by the second operand, and store the value of that bit
into the carry flag. Bit indices are from 0 (least significant) to 15
or 31 (most significant).

   In addition to storing the original value of the bit into the carry
flag, `BTR' also resets (clears) the bit in the operand itself. `BTS'
sets the bit, and `BTC' complements the bit. `BT' does not modify its
operands.

   The destination can be a register or a memory location. The source
can be a register or an immediate value.

   If the destination operand is a register, the bit offset should be
in the range 0-15 (for 16-bit operands) or 0-31 (for 32-bit operands).
An immediate value outside these ranges will be taken modulo 16/32 by
the processor.

   If the destination operand is a memory location, then an immediate
bit offset follows the same rules as for a register. If the bit offset
is in a register, then it can be anything within the signed range of
the register used (ie, for a 32-bit operand, it can be (-2^31) to (2^31
- 1)