# FABS — Absolute Value

Opcode |  | Mode | Leg Mode | Description
--- | --- | --- | --- | ---
D9 E1 |  |  |  | Replace ST with its 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.

ST(0) SRC | ST(0) DEST
--- | ---
−∞ | +∞
−F | +F
−0 | +0
+0 | +0
+F | +F
+∞ | +∞
NaN | NaN

Table 3-17. Results Obtained from FABS

> F Meansfinitefloating-pointvalue.

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.
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.

## 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.