Operation exception is signaled if one or both of the operands are invalid for an implemented operation. When the exception occurs without a trap, the MIPS ISA defines the result as a quiet Not a Number (NaN). The invalid operations are:
- Addition or subtraction: magnitude subtraction of infinities, such as: ( + ) + ( - ) or ( - ) - ( - )
- Multiplication: 0 times , with any signs
- Division: 0/0, or /, with any signs
- Comparison of predicates involving < or > without ?, when the operands are unordered
- Comparison or a Convert From Floating-point Operation on a signaling NaN.
- Any arithmetic operation on a signaling NaN. A move (MOV) operation is not considered to be an arithmetic operation, but absolute value (ABS) and negate (NEG) are considered to be arithmetic operations and cause this exception if one or both operands is a signaling NaN.
- Square root: xd6 x, where x is less than zero
Software can simulate the Invalid Operation exception for other operations that are invalid for the given source operands. Examples of these operations include IEEE Standard 754-specified functions implemented in software, such as Remainder: x REM y, where y is 0 or x is infinite; conversion of a floating-point number to a decimal format whose value causes an overflow, is infinity, or is NaN; and transcendental functions, such as ln (-5) or cos-1(3). Refer to Appendix B for examples or for routines to handle these cases.
Trap Enabled Results: The original operand values are undisturbed.
Trap Disabled Results: A quiet NaN is delivered to the destination register if no other software trap occurs.
