Intel 253666-024US Manuel D’Utilisation

3-288 Vol. 2A

FABS—Absolute Value

INSTRUCTION SET REFERENCE, A-M

FABS—Absolute Value

Description

Clears the sign bit of ST(0) to create the absolute value of the operand. The following 
table shows the results obtained when creating the absolute value of various classes 
of numbers.

This instruction’s operation is the same in non-64-bit modes and 64-bit mode.

Operation

ST(0) ← |ST(0)|;

FPU Flags Affected

C1

Set to 0 if stack underflow occurred; otherwise, set to 0.

C0, C2, C3 

Undefined.

Floating-Point Exceptions

#IS

Stack underflow occurred.

Protected Mode Exceptions

#NM

CR0.EM[bit 2] or CR0.TS[bit 3] = 1.

#UD 

If the LOCK prefix is used.

Opcode

Instruction

64-Bit 

Mode

Compat/

Leg Mode

Description

D9 E1

FABS

Valid

Valid

Replace ST with its absolute value.

Table 3-22.  Results Obtained from FABS 

ST(0) SRC

ST(0) DEST

−

•

+

•

−F

+F

−0

+0

+0

+0

+F

+F

+

∞

+

•

NaN

NaN 

NOTES:

F Means finite floating-point value.