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Re: New Vax - future directions :-)

On 2021-07-06 15:24, Anders Magnusson wrote:
Den 2021-07-06 kl. 11:48, skrev Johnny Billquist:
On 2021-07-06 11:28, Anders Magnusson wrote:

A side note: There is a very interesting part of the instruction set that I think should be investigated more - the packed decimal instructions. Those will in fact implement arbitrary precision in hardware, which could be really nice to have when doing things like crypto calculations etc...

That's an interesting view. I've always looked at the packed decimal stuff as mostly targeted at Cobol and financial applications.

You need to remember, though, that packed decimal strings have at most 31 digits. So not entirely arbitrary. (Hmm, not entirely sure if it is 31 digits, or 31 bytes...)
Well, nothing stops from allowing numbers strings in the future. They are handled like the string instructions, so they can be interrupted. The same with the other string instructions, no reason to have a limit on the string length.

Very true. But the VAX have defined that you get an exception if the length is more than 31. So you'd have to break compatibility at least slightly for this.

But I also wonder if these instructions are rather inefficient. Good for financials though, since you're more interested in not getting the artifacts of floating point in there. And dealing with 31 digits for money seems plenty enough. Even if we have microcents.


Johnny Billquist                  || "I'm on a bus
                                  ||  on a psychedelic trip
email: bqt%softjar.se@localhost             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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