Hi,
replies from the 'masters' :)
well well..

Scott Dattalo wrote:

<snip>
>I just so happen to know that Nikolai is away from his computer at the
moment...
><snip>
>The following section may be shortened slightly in one of two ways:
>
>   rlf   known_zero,w    ;a trick learned from payson
>   addwf Product+2,f
>   rlf   known_zero,w
>   addwf Product+1,f
>   rlf   known_zero,w
>   addwf Product+0,f

Yes I know he is away, still his was kind enough to reply to an e-mail
of mine prior to posting this ( asked if he had any
objections/suggestions, =

which he did not have ).

And yes the 'known zero' trick, I observed that on some code snippets on
the faq site,
very clever, but it's 'harder' to understand the effect =

at first sight. Therefore to make the code somewhat easier to
read I normally leave out such optimisations ( until I really need them
:) ).

But You are correct ofcource.

However this one:

>   skpnc
>    incf  Product+2,f
>   skpnc
>    incf  Product+1,f
>   skpnc
>    incf  Product+0,f

Will not work. Carry not affected by INCF. ( also noted by Bob Ammerman
)

>Thanks for posting this , Tony

If it wasn't for the *active* on this list I would still
be trying to turn on the darn LED :).

Bob Ammerman wrote:

>This looks real good. I especially like the four instruction snippet:
>
>movf    <somebyte>,W
>skpnc
>incfsz    <somebyte>,W
>addwf    <resultbyte>,F
>
>As a slick way to do handle carries in an N-byte multiple precision
add. If
>this trick is well-known, it has somehow escaped me. [James: how about
a
>section on N-byte arithmetic in the code snippets archive?]

Where do you think I got that from :), i.e. I take NO credit from
that part, someone else already thought of it ( Payson ? ).

>I don't understand how this can be true when all accesses to RAM are
byte
>wide and indeed the individual bytes of each value can be anywhere in
memory
>with no change in performance.

Neither do I, but other people has suggested from time to time that
( according to their expirience ) big endian can 'save' a few cycles.
For example Nikolai's code generator will have an variance of a few
cycles
depending on big or little endian, I dont know why but I does.
( that's the one with constant multiplication )

I'll let it rest, no flames please. ( should have left that part out :)
)

/Tony










Tony K=FCbek, Flintab AB            =

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E-mail: tony.kubek@flintab.com
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