Copyright (C) 1994, Digital Equipment Corp.The interface
FloatMode allows you to test the behavior of
rounding and of numerical exceptions. On some implementations it
also allows you to change the behavior, on a per-thread basis.
INTERFACEFloatMode (* FOR IRIX5 *); CONST IEEE = TRUE;
TRUE for fully-compliant IEEE implementations. EXCEPTION Failure;
Raised by attempts to set modes that are not supported by the implementation.
TYPE RoundingMode =
{NearestElseEven, TowardMinusInfinity, TowardPlusInfinity,
TowardZero, NearestElseAwayFromZero, IBM370, Other};
Rounding modes. The first four are the IEEE modes.
CONST RoundDefault = RoundingMode.NearestElseEven;
Implementation-dependent: the default mode for rounding arithmetic
operations, used by a newly forked thread. This also specifies the
behavior of the ROUND operation in half-way cases.
PROCEDURE SetRounding(md: RoundingMode) RAISES {Failure};
Change the rounding mode for the calling thread tomd, or raise the exception if this cannot be done. This affects the implicit rounding in floating-point operations; it does not affect theROUNDoperation. Generally this can be done only on IEEE implementations and only ifmdis an IEEE mode.
PROCEDURE GetRounding(): RoundingMode;
Return the rounding mode for the calling thread.
TYPE Flag = {Invalid, Inexact, Overflow, Underflow,
DivByZero, IntOverflow, IntDivByZero};
Associated with each thread is a set of boolean status flags
recording whether the condition represented by the flag has
occurred in the thread since the flag was last reset. The meaning
of the first five flags is defined precisely in the IEEE floating
point standard; roughly they mean:
\begin{quote}
Invalid = invalid argument to an operation.
Inexact = an operation produced an inexact result.
Overflow = a floating-point operation produced a result whose
absolute value is too large to be represented.
Underflow = a floating-point operation produced a result whose
absolute value is too small to be represented.
DivByZero = floating-point division by zero.
The meaning of the last two flags is:
IntOverflow = an integer operation produced a result whose
absolute value is too large to be represented.
IntDivByZero = integer DIV or MOD by zero.
\end{quote}
CONST NoFlags = SET OF Flag {};
PROCEDURE GetFlags(): SET OF Flag;
Return the set of flags for the current thread.
PROCEDURE SetFlags(s: SET OF Flag)
: SET OF Flag RAISES {Failure};
Set the flags for the current thread to s, and return their
previous values. PROCEDURE ClearFlag(f: Flag);
Turn off the flag f for the current thread.
EXCEPTION Trap(Flag);
TYPE Behavior = {Trap, SetFlag, Ignore};
The behavior of an operation that causes one of the flag conditions
is either:
\begin{quote}
Ignore = return some result and do nothing.
SetFlag = return some result and set the condition flag. For
IEEE implementations, the result of the operation is defined by the
standard.
Trap = possibly set the condition flag; in any case raise the
Trap exception with the appropriate flag as the argument.
\end{quote}
PROCEDURE SetBehavior(f: Flag; b: Behavior) RAISES {Failure};
Set the behavior of the current thread for the flagfto beb, or raiseFailureif this cannot be done.
PROCEDURE GetBehavior(f: Flag): Behavior;
Return the behavior of the current thread for the flag f. ----------------------------------------------------------------- misc. ---
TYPE ThreadState = RECORD
behavior: ARRAY Flag OF Behavior;
sticky: ARRAY Flag OF BOOLEAN;
END;
One copy per thread, saved by the thread implementation.
PROCEDURE InitThread(VAR s: ThreadState);
Initialize the current thread to the default floating-point state.
IRIX5 defaults: RoundingMode = Nearest;
(X => default behavior, @ => allowed by SetBehavior, . => not allowed)
Flag Ignore SetFlag Trap -------- ------------------------- Invalid @ X @ Inexact @ X @ Overflow @ X @ Underflow @ X @ DivByZero @ X @ IntOverflow X . . IntDivByZero . . X
END FloatMode.