A.5.17 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)).