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Re: [avr-libc-dev] Re: Add items on TODO


From: Joerg Wunsch
Subject: Re: [avr-libc-dev] Re: Add items on TODO
Date: Wed, 23 Oct 2002 10:51:40 +0200
User-agent: Mutt/1.2.5i

As Theodore A. Roth wrote:

> Sure. Before I commit it, can you explain what seems to be the problem
> with asin?

It gets suspicious results on small arguments.  Since acos uses asin,
it gets suspicious results on arguments around pi/2.

> My investigation seemed lead to there
> not being a clear understanding of the format of the floats. gcc
> uses ieee format floats so 1.0 looks like 0x3f800000, while the
> asin() implementation seems to think 1.0 is 0x7f000000.

In that case, it looks like a bug in its implementation...

Once i'm finished with the printf() stuff, i thought about having a
closer look at libm.  There are more bogons in it, like exported
interfaces that should not be exported without leading underscores
(see fp_powerseries).  Also, adding some more comments and/or
self-commenting macros wouldn't hurt either...  I've already started
replacing all the magic numbers in dtostre() by cpp-defined macros
that are much easier to verify.  I didn't do that out of the blue :),
but only once i discovered that dtostre() got one of those floating
point constants wrong (which was however mostly benign there).

-- 
J"org Wunsch                                           Unix support engineer
address@hidden        http://www.interface-systems.de/~j/




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