3-171
INSTRUCTION SET REFERENCE
FBSTPStore BCD Integer and Pop
Description
This instruction converts the value in the ST(0) register to an 18-digit packed BCD integer,
stores the result in the destination operand, and pops the register stack. If the source value is a
non-integral value, it is rounded to an integer value, according to rounding mode specified by
the RC field of the FPU control word. To pop the register stack, the processor marks the ST(0)
register as empty and increments the stack pointer (TOP) by 1.
The destination operand specifies the address where the first byte destination value is to be
stored. The BCD value (including its sign bit) requires 10 bytes of space in memory.
The following table shows the results obtained when storing various classes of numbers in
packed BCD format.
NOTES:
FMeans finite-real number.
DMeans packed-BCD number.
*Indicates floating-point invalid operation (#IA) exception.
**
±
0 or
±
1, depending on the rounding mode.
If the source value is too large for the destination format and the invalid operation exception is
not masked, an invalid operation exception is generated and no value is stored in the destination
operand. If the invalid operation exception is masked, the packed BCD indefinite value is stored
in memory.
If the source value is a quiet NaN, an invalid operation exception is generated. Quiet NaNs do
not normally cause this exception to be generated.
Opcode
Instruction
Description
DF /6
FBSTP m80bcd
Store ST(0) in m80bcd and pop ST(0).
ST(0)
DEST
-
?
*
?
F <
?
1
?
D
?
1
<
?
F
<
?
0
**
?
0
?
0
+
0
+0
+0 < +F < +1
**
+F > +1
+D
+
?
*
NaN
*
