3-174
INSTRUCTION SET REFERENCE
FCHS—Change Sign
Description
This instruction complements the sign bit of ST(0). This operation changes a positive value into
a negative value of equal magnitude or vice versa. The following table shows the results
obtained when changing the sign of various classes of numbers.
NOTE:
F Means finite-real number.
Operation
SignBit(ST(0))
<
NOT (SignBit(ST(0)))
FPU Flags Affected
C1
Set to 0 if stack underflow occurred; otherwise, cleared to 0.
C0, C2, C3
Undefined.
Floating-Point Exceptions
#IS
Stack underflow occurred.
Protected Mode Exceptions
#NM
EM or TS in CR0 is set.
Opcode
Instruction
Description
D9 E0
FCHS
Complements sign of ST(0)
ST(0) SRC
ST(0) DEST
??
+
?
?
F
+F
?
0
+
0
+
0
?
0
+F
?
F
+
?
??
NaN
NaN
