fabs

Absolute Value

FABS

Replaces ST(0) with its absolute value.

Pseudocode Operation

ST(0) ← |ST(0)|;

Encoding

Binary Layout

D9

+0

E1

+1

 

Format Legacy

Opcode D9 E1

Extension x87 FPU

Operands

Related

More in x87 FPU

Reference

View in Intel® 64 and IA-32 Architectures SDM ↗ Intel® SDM

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
D9 E1	FABS		Valid Valid		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.

Table 3-19. Results Obtained from FABS

ST(0) SRC ST(0) DEST

- ∞                                                 + ∞
- F                                                 + F
- 0                                                 + 0
+ 0                                                 + 0
+ F                                                 + F

+ ∞ + ∞

NaN NaN

Operation

ST(0) := |ST(0)|;

Exceptions

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. FABS-Absolute Value Vol. 2A 3-309 FABS-Absolute Value Vol. 2A 3-310