FABS (Absolute Value)
Opcodes
Opcode | Instruction | 64-Bit Mode | Compat/Leg Mode | 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 3-27. 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.
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.