[cairo-bugs] [Bug 4846] Performance problems for GTK+/Cairo on MacOS X

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https://bugs.freedesktop.org/show_bug.cgi?id=4846          
     




------- Additional Comments From bogdanni at hotmail.com  2005-10-26 06:01 -------

Doing this fixes it for me (I don't understand why yet). The interface gets drawn fast and correctly.
Notice it consistently rounds away from 0 for both positive and negative half-way cases. The C99 
"round" function should work as well.
Is this the correct behavior? 

cairo_fixed_t
_cairo_fixed_from_double (double d)
{
    if (d < 0.)
        return (cairo_fixed_t) (d * 65536 - .5);
    else
        return (cairo_fixed_t) (d * 65536 + .5);
}

No clue yet why the original breaks. It may have to do with the fact that "d * 65536 + .5" is generated 
as a FMA (fused multiply-add) instruction which doesn't do an intermediate rounding operation.
          
     
     
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