Re: [xml] Test comparison fails on value (-2147483648)

[Daniel Veillard <veillard redhat com>]

On Sun, Aug 26, 2001 at 12:37:55PM -0500, Chris_Poblete Dell com wrote:
> VERSIONS: libxml2-2.4.3
>           libxslt-1.0.3
>
> PROBLEM:
> The tag <xsl:when test="OutputWatts &lt; 0"> fails to evaluate correctly 
> when OutputWatts is equal to -2147483648.  

  Well OutputWatts will evaluate to a nodeset which then once
used in the comparison will end up being casted to a float. OutputWatts
cannot be equal to -2147483648 but it's float value may be equal to this
 value.
  I hope you understand that this compare a set of XML nodes with a value.

> PROPOSED RESOLUTION:
> xpath:xmlXPathStringEvalNumber(6567)
> ------------------------------------------------------------
> <     ret = (double) tmp;
> ----------
> >     ret = (double) tmp;
> >     // Variable tmp is declared as signed integer which may evaluate to
> a negative
> >     // number.  We only need to calculate the absolute value of the
> whole number since
> >     // any negative character in the input string has been flagged
> separately.
> >     if (tmp < 0)
> >             ret = -ret;
> ------------------------------------------------------------

  This looks wrong to me. The sign is caught when beginning to parse
the string:

    if (*cur == '-') {
        isneg = 1;
        cur++;
    }

  Then before returning the value
    if (isneg) ret = -ret;

 If we apply you suggested change we change the sign twice in all cases,
looks wrong to me.
 The problem you're facing is an integer overflow. If you look at the
comment 5 lines before your suggested change you will get the explanation:

    /*
     * tmp is a workaroudn against a gcc compiler bug
     */

I spent a number of hours chasing it down and finding a workaround, your
problem case don't doesn't seems realistic and I would prefer not change
that part of the code.

Daniel

-- 
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