FCHS - Change Sign

Opcode

Instruction

64-Bit Mode

Compat/ Leg Mode

Description

D9 E0

FCHS

Valid

Valid

Complements sign of ST(0).

Description

Complements the sign bit of ST(0). This operation changes a positive value into a negative value of equal magni- tude or vice versa. The following table shows the results obtained when changing the sign of various classes of numbers.

Table 3-20. FCHS Results

ST(0) SRC

ST(0) DEST

- inf

+ inf

- F

+ F

- 0

+ 0

+ 0

- 0

+ F

- F

+ inf

- inf

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 

SignBit(ST(0)) := NOT (SignBit(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.