Re: [Stds-754] motion: update exception and flag operations for consistency

[r754@xxxxxxxxxxxxxx]

        This is item 20 for August.  - Dan

> Date: Wed, 2 Aug 2006 23:11:14 -0700 (PDT)
> From: David Hough 754R work <754r@xxxxxxxxxxx>
> Subject: [Stds-754] motion: update exception and flag operations for
>       consistency
>
>
> Motion:  update exception and flag operations for consistency
>
> Rationale: The style of the exceptions and flags operations interface
> is not consistent with that of
> the mode operations which the committee approved in the motion of Agenda
> item #42 in June.  This proposal addresses just this inconsistency.
>
> Comment:
> In June, motions #18 and #42 were both passed with similar majorities,
> concerning the operations on flags and modes mentioned barely in 754,
> and the operations for signaling exceptions which were more implied than
> mentioned in 754.
>
> Evidently both majorities of voters did not read the motions, did not notice
> certain stylistic discrepancies, or didn't care.    August motion #18 intends
> to reconcile these operations consistent with one point of view,
> and this motion #20 is based upon a different one.
>
> This motion is based upon the point of view that the operations worth
> standardizing are the ones that are important to application programmers
> attempting to build portable applications upon the framework of this
> standard.    Application programs generally know which exceptions and flags
> they want to deal with, and there's no value in forcing them to fit their
> locutions into a more general framework that, if performance is to be obtained
> in higher level languages, optimizing compilers will just have to undo.
> So the standard should point language designers in that direction of
> applicability rather than generality.     But languages remain free to
> implement things in a less convenient way if they prefer.
>
>
> Text:
> Nicely formatted:
> <a 
> href="http://754r.ucbtest.org/motions/simplify-flags.pdf";>http://754r.ucbtest.org/motions/simplify-flags.pdf</a>
>
> Crudely formatted: [DEL] marks strikeout of existing text:
>
>   7.7.2 Exception signaling-computational operations
>
>    Implementations shall provide the following non-computational
>    operations to signal the exceptions specified by their names, invoking
>    either default or, if explicitly requested by the programmer, a
>    language-defined alternate handling:
>
>    - void signalInvalid(void):
>
>    - void signalDivideByZero(void):
>
>    - void signalOverflow(void):
>
>    - void signalUnderflow(void):
>
>    - void signalInexact(void):
>
>    [These are the operations most often used by application programmers,
>    who generally know which exceptions are at issue. The first, for
>    instance, is conceptually equivalent to
>    signalException(invalidException) - and could be defined that way in a
>    language - but not equivalent in performance unless optimizing
>    compilers recognize the programmer's original intent by undoing the
>    indirect locution. There is no need to signal multiple exceptions
>    simultaneously - no 754 operations do so, though they can appear to
>    raise two flags simultaneously - but only in default exception
>    handling.]
>
>    [DEL: This operation signals the exceptions specified by its operand,
>    invoking either default or, if explicitly requested by the programmer,
>    a language-defined alternate handling: :DEL]
>
>    [DEL: - void signalException(exceptionGroupType):
>    signals the exceptions specified in the exceptionGroupType operand,
>    which can represent any subset of the exceptions :DEL]
>
>    [DEL: Whether signalException additionally signals the inexact
>    exception whenever it signals overflow or underflow is language
>    defined. If signalException signals overflow and inexact or underflow
>    and inexact, then it signals overflow or underflow before inexact.
>    Otherwise, the order in which the exceptions are signaled is
>    unspecified. :DEL]
>
>   7.8.4 Operations on individual flags
>
>        Implementations shall provide the following non-computational
>        operations to raise, lower, and test individual status flags:
>
>    - void raiseInvalid(void):
>
>    - void raiseDivideByZero(void):
>
>    - void raiseOverflow(void):
>
>    - void raiseUnderflow(void):
>
>
>    - void raiseInexact(void):
>
>    - void lowerInvalid(void):
>
>    - void lowerDivideByZero(void):
>
>    - void lowerOverflow(void):
>
>    - void lowerUnderflow(void):
>
>    - void lowerInexact(void):
>
>    - boolean testInvalid(void):
>
>    - boolean testDivideByZero(void):
>
>    - boolean testOverflow(void):
>
>    - boolean testUnderflow(void):
>
>    - boolean testInexact(void):
>
>    [These are the operations most often used by application programmers,
>    who generally know which flags are at issue. The first, for instance,
>    is conceptually equivalent to raiseFlag(invalidFlag) - and could be
>    defined that way in a language - but not equivalent in performance
>    unless optimizing compilers recognize the programmer's original intent
>    by undoing the indirect locution. ]
>    [DEL: 7.8.4 Operations on subsets of flags :DEL]
>        [DEL: Implementations shall provide the following
>        non-computational operations that act upon multiple all status
>        flags collectively: :DEL]
>
>    [DEL: - void lowerFlag(exceptionGroupType): :DEL]
>
>    [DEL: lowers (clears) the flags corresponding to the exceptions
>    specified in the exceptionGroupType operand, which can represent any
>    subset of the exceptions :DEL]
>
>    [DEL: - boolean testFlag(exceptionGroupType): :DEL]
>
>    [DEL: queries whether any of the flags corresponding to the exceptions
>    specified in the exceptionGroupType operand, which can represent any
>    subset of the exceptions, are raised :DEL]
>
>    [DEL: - void restoreFlag(flagsType, exceptionGroupType): :DEL]
>
>    [DEL: restores the flags corresponding to the exceptions specified in
>    the exceptionGroupType operand, which can represent any subset of the
>    exceptions, to their state represented in the flagsType operand :DEL]
>
>   7.8.5 Operations on all flags
>
>        Implementations shall provide the following non-computational
>        operations that act upon all status flags collectively:
>
>    - flagsType saveFlags(void)
>    returns a representation of the state of all the flags. The return
>        values of the saveFlags operation are for use as the first operand
>        to the restoreFlag operation in the same program; this standard
>        does not require support for any other use.
>
>    - void restoreFlags(flagsType)
>    restores the state of all the flags. The return values of the
>        saveFlags operation are for use as the operand of the restoreFlags
>        operation in the same program; this standard does not require
>        support for any other use.
>
>    - void lowerFlags(void)
>    lowers all the status flags
>        [These are the operations most often used by system and library
>        programmers.]
>        [DEL: Implementations shall provide the following
>        non-computational operations that act upon all status flags
>        collectively: :DEL]
>
>    [DEL: - flagsType saveFlags(void) :DEL]
>    [DEL: returns a representation of the state of all the flags. The
>        return values of the saveFlags operation are for use as the first
>        operand to the restoreFlag operation in the same program; this
>        standard does not require support for any other use. :DEL]