4:40
Volume 4: Base IA-32 Instruction Reference
BT—Bit Test
Description
Selects the bit in a bit string (specified with the first operand, called the bit base) at the
bit-position designated by the bit offset operand (second operand) and stores the value
of the bit in the CF flag. The bit base operand can be a register or a memory location;
the bit offset operand can be a register or an immediate value. If the bit base operand
specifies a register, the instruction takes the modulo 16 or 32 (depending on the
register size) of the bit offset operand, allowing any bit position to be selected in a 16-
or 32-bit register, respectively. If the bit base operand specifies a memory location, it
represents the address of the byte in memory that contains the bit base (bit 0 of the
specified byte) of the bit string. The offset operand then selects a bit position within the
range
2
31
to 2
31
1 for a register offset and 0 to 31 for an immediate offset.
Some assemblers support immediate bit offsets larger than 31 by using the immediate
bit offset field in combination with the displacement field of the memory operand. In
this case, the low-order 3 or 5 bits (3 for 16-bit operands, 5 for 32-bit operands) of the
immediate bit offset are stored in the immediate bit offset field, and the high-order bits
are shifted and combined with the byte displacement in the addressing mode by the
assembler. The processor will ignore the high order bits if they are not zero.
When accessing a bit in memory, the processor may access 4 bytes starting from the
memory address for a 32-bit operand size, using by the following relationship:
Effective A (4
(BitOffset DIV 32))
Or, it may access 2 bytes starting from the memory address for a 16-bit operand, using
this relationship:
Effective A (2
(BitOffset DIV 16))
It may do so even when only a single byte needs to be accessed to reach the given bit.
When using this bit addressing mechanism, software should avoid referencing areas of
memory close to address space holes. In particular, it should avoid references to
memory-mapped I/O registers. Instead, software should use the MOV instructions to
load from or store to these addresses, and use the register form of these instructions to
manipulate the data.
Operation
CF
Bit(BitBase, BitOffset)
Flags Affected
The CF flag contains the value of the selected bit. The OF, SF, ZF, AF, and PF flags are
undefined.
Opcode
Instruction
Description
0F A3
BT
r/m16,r16
Store selected bit in CF flag
0F A3
BT
r/m32,r32
Store selected bit in CF flag
0F BA /4
ib
BT
r/m16,imm8
Store selected bit in CF flag
0F BA /4
ib
BT
r/m32,imm8
Store selected bit in CF flag
Summary of Contents for ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
Page 1: ......
Page 11: ...x Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 13: ...1 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Page 57: ...1 46 Volume 1 Part 1 Execution Environment ...
Page 147: ...1 136 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 149: ...1 138 Volume 1 Part 2 About the Optimization Guide ...
Page 191: ...1 180 Volume 1 Part 2 Predication Control Flow and Instruction Stream ...
Page 230: ......
Page 248: ...236 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 250: ...2 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 264: ...2 16 Volume 2 Part 1 Intel Itanium System Environment ...
Page 380: ...2 132 Volume 2 Part 1 Interruptions ...
Page 398: ...2 150 Volume 2 Part 1 Register Stack Engine ...
Page 486: ...2 238 Volume 2 Part 1 IA 32 Interruption Vector Descriptions ...
Page 750: ...2 502 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 754: ...2 506 Volume 2 Part 2 About the System Programmer s Guide ...
Page 796: ...2 548 Volume 2 Part 2 Interruptions and Serialization ...
Page 808: ...2 560 Volume 2 Part 2 Context Management ...
Page 842: ...2 594 Volume 2 Part 2 Floating point System Software ...
Page 850: ...2 602 Volume 2 Part 2 IA 32 Application Support ...
Page 862: ...2 614 Volume 2 Part 2 External Interrupt Architecture ...
Page 870: ...2 622 Volume 2 Part 2 Performance Monitoring Support ...
Page 891: ......
Page 1099: ...3 200 Volume 3 Instruction Reference padd Interruptions Illegal Operation fault ...
Page 1295: ...3 396 Volume 3 Resource and Dependency Semantics ...
Page 1296: ......
Page 1302: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1494: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Page 1647: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Page 1884: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Page 1885: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Page 1886: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1898: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...