Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3, Manual

Page: 1488 / 1898

4:186 Volume 4: Base IA-32 Instruction Reference
FSUBR/FSUBRP/FISUBR—Reverse Subtract (Continued)
When the difference between two operands of like sign is 0, the result is +0, except for
the round toward

mode, in which case the result is  0. This instruction also
guarantees that +0  (  0) = +0, and that  0  (+0) =  0. When the source operand is
an integer 0, it is treated as a +0.
When one operand is  , the result is  of the expected sign. If both operands are  of
the same sign, an invalid-operation exception is generated.
Notes:
Fmeans finite-real number.
Imeans integer.
*indicates floating-point invalid-arithmetic-operand (#IA) exception.
Operation
IF instruction is FISUBR
THEN
DEST

ConvertExtendedReal(SRC)

DEST;
ELSE (* source operand is real number *)
DEST

SRC

DEST;
FI;
IF instruction = FSUBRP
THEN
PopRegisterStack
FI;
FPU Flags Affected
C1 Set to 0 if stack underflow occurred.
Indicates rounding direction if the inexact-result exception (#P) fault
is generated: 0 = not roundup; 1 = roundup.
C0, C2, C3 Undefined.
Table 2-10. FSUBR Zeros and NaNs
SRC
 
F

0 + 0 + F +

NaN

* +

+

+

+

+

NaN
DEST

F or

I
 
F or

0

DEST

DEST + F +

NaN

0

SRC

0 +0 SRC +

NaN
+ 0

SRC

0

0 SRC +

NaN
+ F or +I
 
F

DEST

DEST

F or

0 +

NaN
+
     
* NaN
NaN NaN NaN NaN NaN NaN NaN NaN