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Re: [ft-devel] different output from 32-bit and 64bit version of gray_re
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From: |
Alexei Podtelezhnikov |
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Subject: |
Re: [ft-devel] different output from 32-bit and 64bit version of gray_render_scanline |
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Date: |
Thu, 13 Jun 2019 09:21:46 -0400 |
> > > So, is this a surprise to anyone? Should the two versions behave
> > > identically in the absence of overflow or other extreme cases?
> >
> > The behaviour should be identical, yes. Reason for two code paths is
> > velocity.
>
> Yes. The original version involves complex remainder accounting. I
> strongly suspect that it breaks down a bit upon entering
> gray_render_scanline. That function should be aware of the remainder
> above, but it is not. You are welcome to track it down but it is a
> tough code to grasp.
The comments in this commit might help understand the code, if you are
still interested.
https://git.savannah.gnu.org/cgit/freetype/freetype2.git/commit/?id=bdac4cbe6fb77108a753be859fe73579c5cddc97