Legacy apps in Windows/OS X was Re: Old MS-DOS & Win Software

Dwight K. Elvey dwight.elvey at amd.com
Thu Dec 8 18:17:10 CST 2005


>From: "Chuck Guzis" <cclist at sydex.com>
>
>It's a problem with instruction sets that implement result codes as a
>simple condition code register.  The same arithmetic that couints
>interations affects the condition codes that one might also need for
>searching or computation.  That's probably the reason that the increment
>and decrement instructions don't bother the carry flag and that the 16-bit
>increments and decrements on the 8080 didn't bother any of the condition
>codes.  Inspection of the 808x instruction set can be very illuminiating,
>particularly when it comes to arcana like which instructions modify (and
>how) the half-carry flag, for example.
>
>Cheers,
>Chuck

Hi
 I still don't fully understand the decimal fuctions
of the 4004. It has similar problems with addition and
subtraction. It, of course, doesn't have to deal with
a half carry, being only 4 bits.
Dwight





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