The TrueType font format is full of checksums: the directory entry for each table includes a checksum of the table contents, and in addition the checksum for the entire font is supposed to come out to a fixed value. To make the necessary adjustment to the font checksum, there is a longword field in the 'head' table that can be set to any desired value.
Unfortunately, this field gets counted in the font checksum twice, so it can only adjust its value by ±2. So if you have an odd number of tables with odd content checksums, there seems to be no way to get the overall font checksum to come out right. Back when I was mucking around with Macintosh fonts, I used to come across a lot of ones with bad checksums--seems like font creators couldn’t even be bothered to get them right. But there is a way to do this: what I did in my font-hacking tools was, where necessary, add an extra longword to the font that was not part of any table. This way, it didn’t get counted in any table checksum, but only in the overall font checksum. Setting this field to 1 served to even out the odd content checksums, so the overall font checksum could be made to come out correct. _______________________________________________ Freetype mailing list [email protected] https://lists.nongnu.org/mailman/listinfo/freetype
