Sujet : Re: Decrement And Branch
De : ldo (at) *nospam* nz.invalid (Lawrence D'Oliveiro)
Groupes : comp.archDate : 14. Aug 2024, 09:53:22
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <v9hra1$csca$6@dont-email.me>
References : 1 2 3
User-Agent : Pan/0.159 (Vovchansk; )
On Wed, 14 Aug 2024 01:33:32 +0000, MitchAlsup1 wrote:
On Tue, 13 Aug 2024 22:00:12 +0000, Lawrence D'Oliveiro wrote:
On Tue, 13 Aug 2024 09:00:25 -0000 (UTC), I wrote:
>
However, the good old VAX (in its usual kitchen-sink fashion) had a
whole set of variations, including one that decremented down to -1
instead of zero. And the Motorola 68000 family only had the decrement
down to -1 version.
>
VAX example of how to use SOBGEQ instead of SOBGTR:
>
movl «loop count», Rn br bottom_of_loop
top_of_loop:
.... body of loop ...
bottom_of_loop:
sobgeq Rn, top_of_loop
>
Like I said, I wondered why this sort of thing wasn’t more common ...
Perhaps the RISC mantra has permeated the minds of ISA designers.
Would you prefer it with a decrement+separate conditional-jump instruction
pair?
Decrement And Branch
Re: Decrement And Branch