x86 Instruction Set Reference

FABS

Absolute Value

Opcode	Mnemonic	Description
`D9 E1`	`FABS`	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.

Results Obtained from FABS
ST(0) Source	ST(0) Destination
-inf	+inf
-F	+F
-0	+0
+0	+0
+F	+F
+inf	+inf
NaN	NaN
NOTE: F Means finite floating-point value.

Operation
ST(0) = GetAbsoluteValue(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 EM or TS in CR0 is set.

Real-Address Mode Exceptions

#NM EM or TS in CR0 is set.

Virtual-8086 Mode Exceptions

#NM EM or TS in CR0 is set.

Instruction	Latency	Throughput	Execution Unit
`CPUID`	0F3n/0F2n	0F3n/0F2n	0F2n
`FABS`	3/2	1/1	FP_MISC