FABS—Absolute ValueDescriptionClears 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.OperationST(0) := |ST(0)|;FPU Flags AffectedC1Set to 0.C0, C2, C3 Undefined.Floating-Point Exceptions#ISStack underflow occurred.Protected Mode Exceptions#NMCR0.EM[bit 2] or CR0.TS[bit 3] = 1.#UD If the LOCK prefix is used.Real-Address Mode ExceptionsSame exceptions as in protected mode.Virtual-8086 Mode ExceptionsSame exceptions as in protected mode.Compatibility Mode ExceptionsSame exceptions as in protected mode.64-Bit Mode ExceptionsSame exceptions as in protected mode.OpcodeInstruction64-Bit ModeCompat/Leg ModeDescriptionD9 E1FABSValidValidReplace ST with its absolute value.Table 3-17. Results Obtained from FABS ST(0) SRCST(0) DEST− ∞+ ∞− F+ F− 0+ 0+ 0+ 0+ F+ F+ ∞+ ∞NaNNaN NOTES:FMeans finite floating-point value.
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