10 Apr
2026
10 Apr
'26
3:58 p.m.
On Apr 10, 2026, at 9:51 AM, Johnny Billquist
<bqt(a)softjar.se> wrote:
On 10/04/2026 15.46, Paul Koning wrote:
Thanks. That makes sense. About Tops-10 and NSP - a bit surprising, considering that all
other implementations manage to do it without FP.
I heard it from the guy who did that, their rep on the DECnet review committee, not having
any luck remembering his name right now. My impression is that he did it because he
could, sort of for hack value, rather than because it was necessary. The NSP spec
actually hints pretty well at ways to do it in integer arithmetic, a moving average with
weight 2^n - 1 is an easy shift and add type of thing.
paul
On Apr
10, 2026, at 9:18 AM, Johnny Billquist <bqt(a)softjar.se>wrote;wrote:
On 10/04/2026 05.30, Terri Kennedy wrote:
Same in RSTS. If FPP exists
the kernel will context switch the FP state, if the currently executing program has set
the flag to ask the kernel to do that. Apart from that, nothing uses it and the kernel
itself doesn't care about the FPP. The only OS I can think of that actually using
floating point in the kernel is TOPS-10; I was told DECnet-10 uses it in the NSP delay
estimation algorithm. On 2026-04-09 09:24, Dave McGuire wrote:
> /me slaps forehead
>
> The 11/70's FP board set is flaky, and it has been removed pending
> repair. I had forgotten about that. But the "hello world" program
> shouldn't use any FP instructions..?
Be careful with bad FP and modern(ish) RSTS/E. It will use FP
(and CIS, for that matter) in the monitor, and if your boards are
returning garbage, you can scarfle* your system disk.
I know (heard) that CIS would be used for copying memory around, but what in the kernel
would depend on FPP?
(A little surprising is that RSX don't, however, it will use the blockmove
instruction of the Mentec processors that have that one.)
In RSX, it only is a topic for context switching and trap handling. The kernel don't
depend on the actual behavior more than in the most basic sense otherwise (auto
increment/decrement being done with the right amounts, and only the actual registers
referred to being changed when expected, and so on.