Thread: 68k details
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Old 23 August 2018, 17:50   #185
meynaf
son of 68k
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Join Date: Nov 2007
Location: Lyon / France
Age: 46
Posts: 3,603
Quote:
Originally Posted by ross View Post
In no particular order, and some are of very little usefulness (and if I think about it better, surely others would come):
How strange, most of them are suggestions i made quite a long time ago


Quote:
Originally Posted by ross View Post
- a scrambler for bytes position (ok 'swap', but is so limited..)
Coldfire's byterev ?
Move to/from register parts ?
(Generic byte scrambler inside registers would have a big shortcoming : must transfer from memory to register before moving at right place.)


Quote:
Originally Posted by ross View Post
- a byte indexer (something like d(ax,dx.b))
Oh yeah ! Missing since the first day i started coding on 68000 !
(Besides, i would prefer an unsigned version.)


Quote:
Originally Posted by ross View Post
- a better usage for the low bit bcc offset (in a word-aligned architecture why permit to jmp on odd adress?!?); yes I know this is not so simple but sure possible
The design reason was that they didn't want to close the door to byte encoding...


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Originally Posted by ross View Post
- a quick form for variable shift/rol operation on [ea]
Quite useful. But not really encodable in a clean way for 68k.


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Originally Posted by ross View Post
- a bits.x 'flipper', for fast mirror effect
Like coldfire's bitrev instruction, but extended to all 3 sizes ?


Quote:
Originally Posted by ross View Post
- some simple form of bitfield instruction (but 020+ covered it in a very good way )
Reverse mode added to bitfields, for counting like btst ?


Quote:
Originally Posted by ross View Post
- an scc for set a single bit can be useful
I have bs<cc> macros in some include file
Main problem for this one is to find an encoding.


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Originally Posted by ross View Post
- ALU instructions with saturation
Like convert longword to signed/unsigned byte or word ?


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Originally Posted by ross View Post
- cmove
Hmm... The only one i don't see the point.
After all, it's just a branch around a move...
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