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September 2007
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2007.09.20 22:20 "Re: libtiff4, and the size of STRIPOFFSETs and TILEOFFSETs", by Andrey Kiselev
On Thu, Sep 20, 2007 at 05:03:57PM -0400, Frank Warmerdam wrote: > I discovered a problem today with GDAL's use of libtiff4. The problem > occurs because libtiff decides as it is writing directories whether to > write fields like TILEOFFSETs as LONG (4byte) or LONG8 (8byte). > However, my code depends on the questionable assumption that I can > rewrite a directory after altering (only) the tile/strip offset and > size values. > > This apparently used to be true, but now it may happen that the > offsets switch from using LONG to LONG8. > > How important is this dynamic behavior? > > I have taken the liberty of changing tif_dirwrite.c so that for > BigTIFF files the tile/strip sizes and offsets are always written as > LONG8. (r1.58 of tif_dirwrite.c) in order to resolve my GDAL > problems. > > I have done so by altering the semantics of > TIFFWriteDirectoryTagLongLong8Array(). I believe it used to write the > array of values as LONG if possible, otherwise write as LONG8 (if > values are too large). Now it basically just writes as LONG for > classic tiff, and as LONG8 for bigtiff. It also does some checking to > confirm that larger than LONG values aren't being written to classic > tiff. Hmm... I think it is not important for the current state of libtiff4, but it should be important for automatic switching between Classic TIFF and Big TIFF writing. Best regards, Andrey -- Andrey V. Kiselev ICQ# 26871517