Re: [xml] XPath mod operator problems

[Justin Fletcher <justin fletcher ntlworld com>]

In message <15643 13793 243565 537255 guitars rock roll>
          Geert Kloosterman <geertk ai rug nl> wrote:

> Hi Daniel, all,
[snip]
> When I change the following lines of xpath.c (l. 4890, 4891),
> xmlXPathModValues:
>
>         tmp=arg1/arg2;
>         ctxt->value->floatval = arg2 * (tmp - (double)((int)tmp));
>
> into
>
>         ctxt->value->floatval = fmod(arg1, arg2);
>
> the behaviour looks correct.  But I don't know if fmod conforms
> to the XPath requirements of the `mod' operator.

I don't think anyone has replied with the standards on these; I only have C
ISO/IEC 9899:1999 to hand, but the relevant section is 7.12.10.2 and
7.12.10.3 :

--8<--------
2    The fmod functions compute the floating-point remainder of x/y.

3    The fmod functions return the value x - ny, for some integer n such
     that, if y is nonzero, the result has the same sign as x and magnitude
     less than the magnitude of y. If y is zero, whether a domain error
     occurs or the fmod functions return zero is implementation-defined.
--8<--------

XPath 1.0 states :

--8<--------
The mod operator returns the remainder from a truncating division.  For
example,

 * '5 mod 2' returns '1'
 * '5 mod -2' returns '1'
 * '-5 mod 2' returns '-1'
 * '-5 mod -2' returns '-1'

Note: This is the same as the % operator in Java and ECMAScript.

This is not the same as the IEEE 754 remainder operation, which
returns the remainder from a rounding division.
--8<--------

This would appear to me to be compatible, and thus suitable for use.
I haven't got earlier versions of the spec but I believe that the
fmod function has been part of the standard library for some time.

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