[Info-vax] Y3K for PDP-11 Operating Systems

[Johnny Billquist]

On 2011-05-10 07.29, Bob Koehler wrote:
> In article<iqa4rr$ebl$1 at Iltempo.Update.UU.SE>, Johnny Billquist<bqt at softjar.se>  writes:
>>
>> Hmm. Memory alignment issues... Good point.
>> Otherwise, I'm also pretty sure that a function like strcpy() is much
>> better to do on your own, as the VAX really don't have a good way of
>> implementing that. Doing first a LOCC to get the length, and then a MOVC
>> to move the string will surely be less efficient than just doing a MOV
>> followed by a conditional branch to loop... Obviously, for C stuff,
>> anything dealing with strings is opposed to how a VAX wants things. :-)
>
>     I never did understand why the VAX C RTL did a LOCC first, instead of a
>     MOVTUC with a straight-through translation table and null escape
>     charater.  I assumed MOVTUC was even slower.

I'm pretty sure that on later machines, MOVTUC is an emulated 
instruction, so you don't want to use it unless you really want the 
special features. For the simple C string case, having that translation 
table is a small memory cost, but it also hurts performance.
But from a purity point of view, yes, MOVTUC should also be able to do it.

>     The need to find that null character, in any case, always seemed to be
>     one more reason to use a better HLL.

:-)

	Johnny