Re: [ft] Correct TrueType Checksums

[Werner LEMBERG]

> The TrueType font format is full of checksums: [...]

FreeType completely ignores them except for a very special purpose,
namely to identify `tricky' (CJK) fonts that must not be auto-hinted
(cf. function `tt_synth_sfnt_checksum' in file `ttobjs.c') – and even
here we don't trust the value in the font but compute it by ourselves
for the `cvt', `fpgm', and `prep' tables only.

> 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.

What do you want to achieve?

> 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.

You might use the `ttx' program to check and/or fix checksums.  AFAIK,
it computes them correctly.


    Werner