[Coco] Is the 6809 is flawed?

Joel Rees joel.rees at gmail.com
Sun Sep 23 07:50:13 EDT 2018

2018年9月8日(土) 8:12 Gene Heskett <gheskett at shentel.net>:

> For twos-complement, it works correctly, in both the 6809 and the 6309.
> I've used both shifts extensively and have never failed to get the
> expected result.
> That I think is one of the drivers for the sex instruction, but have yet
> to see the utility in it since the input data is expected to be correct.
> In any event, I'd check for bad data BEFORE I applied the sex
> instruction. There must be a reason since the C compiler uses it just to
> be boring, and is an instruction I usually skip when doing my personal
> optimizations of the C compilers output.

I have tended to think of the naming of the sign extend instruction as a
marketing mistake.

Engineers find it amusing or bemusing, but managers, spouses, and parents
of underaged geniuses not so much.

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