If I remember correctly, the arithmetic is done with floating 64b numbers, right? Doing bitwise operations there sound a bit (pun intended) strange. I know a bit portion of images used are RGB (byte images), there bitwise operatios are fine.
On Wed, 3 Dec 2025 at 21:14, Even Rouault via gdal-dev < [email protected]> wrote: > I see there's a mu::ParserInt class in > https://github.com/beltoforion/muparser/blob/master/include/muParserInt.h > , that we don't use in GDAL. A bit strange it wasn't mentionned in [1]. > Perhaps because of this comment: "This version of the parser handles only > integer numbers. It disables the built in operators thus it is slower than > muParser. Integer values are stored in the double value_type and converted > if needed." > Le 03/12/2025 à 21:07, Daniel Baston via gdal-dev a écrit : > > Hugh, > > My read of this discussion [1] is that bitwise operators are not supported > and we would need to add them as a GDAL extension. This is pretty easy to > do: see [2]. Alternatively, bitwise operators are probably supported by the > ExprTk expression parser [3] (supported by GDAL) or this pull request [4]. > > Dan > > [1] > https://github.com/beltoforion/muparser/discussions/154#discussioncomment-13104418 > [2] https://github.com/OSGeo/gdal/pull/13187/files > [3] https://www.partow.net/programming/exprtk/ > [4] https://github.com/OSGeo/gdal/pull/13470 > > On Wed, Dec 3, 2025 at 2:58 PM Hugh Graham via gdal-dev < > [email protected]> wrote: > >> Hi, >> >> I am using VRT muparser expressions for bitwise operations when creating >> masks and wanted to understand why I can't get the *bitwise & *operator >> working? My current solution is to use fmod which is fine (and I think >> equivalent) but using "&" would be convenient and a bit easier to read... >> >> To illustrate, the following file works: >> >> https://gist.github.com/h-a-graham/6db16e70e064ae8173f1052537c59761#file-fmask-fmodmask-vrt >> >> the expression used here is:"(fmod(Fmask, 16) >= 8) || (fmod(Fmask, 8) >= >> 4) ? 0 : 1" >> >> ``` >> gdal convert "/vsicurl/ >> https://gist.githubusercontent.com/h-a-graham/6db16e70e064ae8173f1052537c59761/raw/c48b15852bcc7c5252cae4b906c14b9a3205a33d/fmask-fmodmask.vrt"; >> "test.tif" >> ``` >> >> However, the following file fails: >> >> https://gist.github.com/h-a-graham/6db16e70e064ae8173f1052537c59761#file-fmask-bitmask-vrt >> the expression parsed as: "((Fmask & 8) > 0 || (Fmask & 4) >> > 0) ? 0 : 1" in the XML but provided as (to my xml parser): >> >> "((Fmask & 8) > 0 || (Fmask & 4) > 0) ? 0 : 1" >> >> ``` >> gdal convert "/vsicurl/ >> https://gist.githubusercontent.com/h-a-graham/6db16e70e064ae8173f1052537c59761/raw/c48b15852bcc7c5252cae4b906c14b9a3205a33d/fmask-bitmask.vrt"; >> "test.tif" >> 0...10...20..ERROR 1: Unexpected token "& 8) > 0 || (Fmask & 4) > 0) ? 0 >> : 1 " found at position 8. >> ``` >> >> So, is using "&" possible, or should I just stick with fmod and not worry >> about it? >> >> Any help would be much appreciated. >> >> Hugh >> >> >> >> >> >> >> _______________________________________________ >> gdal-dev mailing list >> [email protected] >> https://lists.osgeo.org/mailman/listinfo/gdal-dev >> > > _______________________________________________ > gdal-dev mailing > [email protected]https://lists.osgeo.org/mailman/listinfo/gdal-dev > > -- http://www.spatialys.com > My software is free, but my time generally not. > > _______________________________________________ > gdal-dev mailing list > [email protected] > https://lists.osgeo.org/mailman/listinfo/gdal-dev >
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