Hi Jim, > I was aware that the code was playing with overflow fire when I ported > it a while back. I figured the real fix was to eventually switch to > float instead, as per your last suggestion - at least for the line > widening code. Any takers?
Yeah I can do this, but it will surely take some time. In the meantime, should we push the proposed fix as an interim solution? /Roman > > ...jim > > Roman Kennke wrote: > > Hi there, > > > >> 4. StrokeShapeTest: createStrokedShape() behaves differently. > > > > It turns out that there is an arithmetic overflow here. The pisces > > stroker does a stupid thing here. First it initializes the > > scaledLineWidth like this: > > > > this.scaledLineWidth2 = ((long)transform.m00*lineWidth2); > > > > which is infact wrong, because in fixed point arithmetics you need to > > apply >> 16, because the decimal moves. > > > > However, in another place it uses this factor like this: > > > > dx = (int)( (ly*scaledLineWidth2)/ilen >> 16); > > dy = (int)(-(lx*scaledLineWidth2)/ilen >> 16); > > > > which makes it ok in the end. The only problem is, that we start with an > > incredibly large number, then multiply another incredibly large number > > and _after_ that (when the overflow already occured) do the >> 16. The > > patch moves the >> 16 to the initialization of scaledLineWidth, which > > makes it clearer, more correct and even a tad faster, because we do the > > second calculation at least 2x. > > > > Of course, the real fix here would be to turn the whole implementation > > into floating point. This particular testcase is fixed by this patch, > > and the 'range of correct behaviour' is much large now, but if you deal > > with very large numbers in your shapes, then you will get trouble again. > > > > /Roman > > -- Dipl.-Inform. (FH) Roman Kennke, Software Engineer, http://kennke.org aicas Allerton Interworks Computer Automated Systems GmbH Haid-und-Neu-Straße 18 * D-76131 Karlsruhe * Germany http://www.aicas.com * Tel: +49-721-663 968-48 USt-Id: DE216375633, Handelsregister HRB 109481, AG Karlsruhe Geschäftsführer: Dr. James J. Hunt
