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Date:	Thu, 19 Feb 2004 11:58:38 -0600
From:	Eric Rudd <rudd AT cyberoptics DOT com>
Subject:	Re: C99 Functions Under Development and Checkout
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Kbwms AT aol DOT com wrote:

>In a message dated 2/18/2004 10:42:56 AM Eastern Standard Time, 
>rudd AT cyberoptics DOT com writes:
>
>>ince, for example, inf/inf is outside the domain over which the arc 
>>tangent function is defined, it would seem that a domain error should occur.
>>
>It is not clear to which function you are referring.  The case atan2(Y, X) is 
>handled in the standard:
>
>       If Y is +-Inf and X is -Inf, +-3pi/4 shall be returned.
>       If Y is +-Inf and X is +Inf, +-pi/4 shall be returned.
>
I am referring to the arc tangent function, as it is understood by 
mathematicians.  The behavior of atan2() is defined in Annex F for 
implementations conforming to IEC60559 (which is where you quoted from, 
I'm guessing), but I interpret the 7.12.1 clause as specifying a domain 
error when the corresponding mathematical function is undefined -- hence 
the reference to mathematics.  The mathematical arc tangent function is 
not defined for an undefined argument, so there would seem to be a 
contradiction between that and Annex F.

-Eric Rudd

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