Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1488

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
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.
Table 2-10.
DEST
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
C0, C2, C3
4:186
mode, in which case the result is 0. This instruction also

FSUBR Zeros and NaNs
  F

* +
 F or  I   F or  0
 0 
SRC

+ 0 SRC
  F
+ F or +I
+   
NaN NaN NaN
Set to 0 if stack underflow occurred.
Indicates rounding direction if the inexact-result exception (#P) fault
is generated: 0 = not roundup; 1 = roundup.
Undefined.
SRC
 0
+ 0 + F
+ 
+ +
 DEST  DEST
+ F
 0
+0 SRC
 0  0
SRC
 DEST  DEST  F or  0
  
NaN NaN NaN
Volume 4: Base IA-32 Instruction Reference
+ 
NaN
+ 
NaN
+ 
NaN
+ NaN
+ NaN
+ NaN
* NaN
NaN NaN