DCPU-16 includes 8 general registers named A, B, C, X, Y, Z, I and J. It's a bit of a programmer "trope" to use I and J for loop counters. In DCPU-16, are I and J specialized registers, that should only be used in loops - or do they all end up the same colour in the end?

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    As far as I know the only official docs are here: 0x10c.com/doc/dcpu-16.txt . So not sure you can get an answer unless Notch himself visits this site :-) My guess would be that they are not "reserved" registers and that they all are general purpose. – Ville Krumlinde Apr 4 '12 at 14:15
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    The interpreter is 140 lines of C code, don't hesitate to have a look-see. No, nothing special about those registers. – Hans Passant Apr 4 '12 at 14:35
  • @HansPassant Where is this interpreter? – Ville Krumlinde Apr 4 '12 at 15:41
  • At github, follow the google link. – Hans Passant Apr 4 '12 at 16:06
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    @HansPassant Do you refer to this one: github.com/swetland/dcpu16/blob/master/dcpu.c ? It's an unofficial implementation so I'd say it's not 100% guaranteed to run like the "real thing". But since it follows the spec and the spec does not say anything about special registers I agree it should be ok. – Ville Krumlinde Apr 4 '12 at 16:54

Everything points out to the DCPU-16's eight main registers being "general purpose": while they are 'intended' for a certain use, programmers can use them as they will. The x86 has a similar architecture for its general registers.

The only special purpose registers on DCPU-16 are SP, PC and O.

Edit: The DCPU 1.3 specification introduces a single instruction (MVI) that adds 1 to both I and J after executing, with the intention of being used as a fast memory copy. Notch has expressed disliking this, so it might be eventually dropped, but now I and J are a bit special.

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    The intention of the x86 registers is encoded in the instruction set-- if you use them as they were originally imagined to be used, instructions tend to fit in 1 byte. swansontec.com/sregisters.html has a full treatment – rmmh Apr 4 '12 at 19:21
  • Today I learned, etc, etc. – zaratustra Apr 7 '12 at 11:43

I'm sure conventions will emerge but the instruction set is completely orthogonal with respect to the registers A, B, C, X, Y, Z, I and J so there is no difference between them inherent in the DCPU-16.

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