Freescale Semiconductor MCF5480 - Manual (Page 211)

Floating-Point Exceptions
MCF548x Reference Manual, Rev. 3
Freescale Semiconductor 6-21
6.6.1.4 Operand Error (OPERR)
The operand error exception encompasses problems arising in a variety of operations, including errors too
infrequent or trivial to merit a specific exception condition. Basically, an operand error occurs when an
operation has no mathematical interpretation for the given operands. Table 6-15 lists possible operand
errors. When one occurs, FPSR[OPERR] is set.
Table 6-16 describes results when the exception is enabled and disabled.
6.6.1.5 Overflow (OVFL)
An overflow exception is detected for arithmetic operations in which the destination is a floating-point
data register or memory when the intermediate result’s exponent is greater than or equal to the maximum
exponent value of the selected rounding precision. Overflow occurs only when the destination is S- or
D-precision format; overflows for other formats are handled as operand errors. At the end of any operation
that could potentially overflow, the intermediate result is checked for underflow, rounded, and then
checked for overflow before it is stored to the destination. If overflow occurs, FPSR[OVFL,INEX] are set.
Even if the intermediate result is small enough to be represented as a double-precision number, an
overflow can occur if the magnitude of the intermediate result exceeds the range of the selected rounding
precision format. See Table 6-17 .
Table 6-15. Possible Operand Errors
Instruction Condition Causing Operand Error
FADD [(+
∞) + (-∞)] or [(-∞) + (+∞)]
FDIV (0 ÷ 0) or (
∞ ÷ ∞)
FMOVE OUT (to B, W, or L) Integer overflow, source is NAN or ±
∞
FMUL One operand is 0 and the other is ±
∞
FSQRT Source is < 0 or -
∞
FSUB [(+
∞) - (+∞)] or [(-∞) - (-∞)]
Table 6-16. OPERR Exception Enabled/Disabled Results
Condition OPERR Description
Exception
disabled
0 When the destination is a floating-point data register, the result is a double-precision NAN, with
its mantissa set to all ones and the sign set to zero (positive).
For a FMOVE OUT instruction with the format S or D, an OPERR exception is impossible. With
the format B, W, or L, an OPERR exception is possible only on a conversion to integer overflow,
or if the source is either an infinity or a NAN. On integer overflow and infinity source cases, the
largest positive or negative integer that can fit in the specified destination size (B, W, or L) is
stored. In the NAN source case, a constant of all ones is written to the destination.
Exception
enabled
1 The result written to the destination is the same as for the exception disabled case unless the
exception occurred on a FMOVE OUT, in which case the destination is unaffected. If desired,
the user OPERR handler can overwrite the default result.