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.
