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Sender: rich AT phekda DOT freeserve DOT co DOT uk
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Date: Sun, 09 Nov 2003 09:35:18 +0000
From: Richard Dawe <rich AT phekda DOT freeserve DOT co DOT uk>
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To: DJGPP workers <djgpp-workers AT delorie DOT com>
Subject: Re: C99 Functions Under Development and Checkout
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Reply-To: djgpp-workers AT delorie DOT com

Hello.

KB Williams wrote:
> Rich Dawe:
>
> In a message dated 11/8/2003 7:09:46 AM Eastern Standard Time,
> rich AT phekda DOT freeserve DOT co DOT uk writes:
>
> > Do the maths functions use get_math_errhandling, to get the value of
> > math_errhandling? Or do they just read math_errhandling? If they look
> > at math_errhandling, then get_math_errhandling is useless. The library
> > user could modify math_errhandling, making the value returned by
> > get_math_errhandling completely bogus.
>
> Functions get_math_errhandling() and set_math_errhandling() are meant
> to be used by external programs.  For example, the test programs
> in the cygnus subdirectory will probably call set_math_errhandling()
> with MATH_ERRNO as a parameter.
>
> The only way to retrieve the original value of math_errhandling is through
> get_math_errhandling().  The global variable math_errhandling can be set
> exactly once during the life of the program.  Thereafter, it cannot be
> reset; any attempt to do so at runtime either by resetting the global
> variable or by calling set_math_errhandling() again will fail.  

It won't fail. The change will just be ignored. E.g.:

    some_maths_function();
    math_errhandling = MATH_ERRNO;

> The math functions use the other two functions, raise_except()
> and set_errno().  Each call to these functions will freshen the original
> value of math_errhandling.
>
> The code tells the story.  It should have been attached to your email.

It was. I read it.

You missed my point. My point was that by making math_errhandling a macro that
calls a function to return the math error handling method(s), you stop the
user from being able to modify math_errhandling. I.e.: the following code will
not compile:

    some_maths_function();
    math_errhandling = MATH_ERRNO;

Summary: Advantages of using a macro to call the get function:

* User cannot modify math_errhandling.
* The code is clearer (no copying of local setting to global setting).

Bye, Rich =]

-- 
Richard Dawe [ http://www.phekda.freeserve.co.uk/richdawe/ ]

"You can't evaluate a man by logic alone." -- McCoy, "I, Mudd", Star Trek