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On 3 January 2015 at 05:33, Dirk Laurie <> wrote:
> The 9th bit in B and C is used to distinguish between constants and registers,
> so your machine will on all instructions that use RK() be able to access only
> half of your registers. That's all of the arithmetic instructions and
> quite a few

I see.

> more. So you might as well reduce SIZE_A to 7 and accept that you have
> a 7-bit machine with a 9-bit opcode space rather than an 8-bit machine with
> a 6-bit opcode space.

I don't follow above - are you suggesting?

#define SIZE_C          8
#define SIZE_B          9
#define SIZE_A          7
#define SIZE_OP       8

This would still allow only 8 bits for C. Unless you are suggesting:

#define SIZE_C          9
#define SIZE_B          9
#define SIZE_A          7
#define SIZE_OP       7

Thanks and Regards