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Re: fix for expt bug

From: Mark H Weaver
Subject: Re: fix for expt bug
Date: Wed, 03 Nov 2010 11:32:28 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.1 (gnu/linux)

Hi Ramakrishnan,

We're almost there, but you neglected one of the comments I made about
your previous patch.

> +      /* If base is negative, expt needs to find -x^n = (-1^n) * (x^n).
> +         We find x^n and then if n is odd, we also multiply the result
> +         with -1. These changes apply only for cases where n is an
> +         integer.
> +      */

I repeat: In the equation above, -x^n parses as -(x^n), but it should be
(-x)^n.  Same problem with (-1^n).  Exponentiation has higher precedence
than negation.

The equation above should be:  (-x)^n = (-1)^n * x^n

Feel free to add more parentheses if you like, but the ones I have
included are essential and must not be removed.

Everything else looks good to me.


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