Intel 253666-024US Manuel D’Utilisation

3-324 Vol. 2A

FFREE—Free Floating-Point Register

INSTRUCTION SET REFERENCE, A-M

FFREE—Free Floating-Point Register

Description

Sets the tag in the FPU tag register associated with register ST(i) to empty (11B).
The contents of ST(i) and the FPU stack-top pointer (TOP) are not affected.
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.

Operation

TAG(i) ← 11B;

FPU Flags Affected

C0, C1, C2, C3 undefined.

Floating-Point Exceptions

None.

Protected Mode Exceptions

#NM

CR0.EM[bit 2] or CR0.TS[bit 3] = 1.

#MF

If there is a pending x87 FPU exception.

#UD

If the LOCK prefix is used.

Real-Address Mode Exceptions

Same exceptions as in protected mode.

Virtual-8086 Mode Exceptions

Same exceptions as in protected mode.

Compatibility Mode Exceptions

Same exceptions as in protected mode.

64-Bit Mode Exceptions

Same exceptions as in protected mode.

Opcode

Instruction

64-Bit

Mode

Compat/

Leg Mode

Description

DD C0+i

FFREE ST(i)

Valid

Sets tag for ST(i) to empty.