Proposed D & DR instructions of the week 
Author Message
 Proposed D & DR instructions of the week

A Glenn Herrmannsfeldt proposed D and DR, as well as SRDA, as instructions
of the week.

If we are going to do D and DR, we should also talk about M and MR if
we are going to talk about SRDA.

If we work something up, I think it should be combined with something
really obscure, namely the Intger and Scaling operand attributes, which
actually work out very well, provided you understand exactly what they
mean.

Anyone have any comments?

Actually, this is a very minor chance to blow a very minor horn.

It is quite possible I was the first person to propose the idea of
making these attributes available in open code.

It happened in 1977 at the summer Share in Washington.  I was sitting in
on a session with the author of the Assembler H extensions, which were
80% of the first HLASM release, and suggested it there to Greg Mushial.
Do I have that name right?  I had tried them with regular IEV90, and
had been blown out of the water.  This was still in my head when I went
to DC for that Share.

-- Steve Myers

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Thu, 18 Jan 2001 03:00:00 GMT  
 Proposed D & DR instructions of the week

Quote:

> If we are going to do D and DR, we should also talk about M and MR if
> we are going to talk about SRDA.

Also the fact that a right shift is not the same as a division on a 2s
complement machine.

Quote:
> It happened in 1977 at the summer Share in Washington.  I was sitting in
> on a session with the author of the Assembler H extensions, which were
> 80% of the first HLASM release, and suggested it there to Greg Mushial.
> Do I have that name right?

Yes.

--

Shmuel (Seymour J.) Metz
Reply to host nsf (dot) gov, user smetz



Thu, 18 Jan 2001 03:00:00 GMT  
 Proposed D & DR instructions of the week

Quote:
>This is a cryptographically signed message in MIME format.
[snip]
>Did anyone notice the non-orthogonality of the instruction set
>where MH has no corresponding divide instruction?

True enough.  If we talk about M and MR, then we must also talk MH and MHI.
Personally, I never thought much about not having something like a
DH.  I suspect it's not there because D and DR are not used all that
much, compared to M and MR.  I do not think there is a DHI instruction
to match the MHI instruction either.

-- Steve Myers

The E-mail addresses in this message are private property.  Any use of them
to  send  unsolicited  E-mail  messages  of  a  commerical  nature  will be
considered trespassing,  and the originator of the message will be  sued in
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allowed by law.



Fri, 19 Jan 2001 03:00:00 GMT  
 Proposed D & DR instructions of the week
(someone wrote)

Quote:
>True enough.  If we talk about M and MR, then we must also talk MH and MHI.
>Personally, I never thought much about not having something like a
>DH.  I suspect it's not there because D and DR are not used all that
>much, compared to M and MR.  I do not think there is a DHI instruction
>to match the MHI instruction either.

The reason I didn't include M and MR in the original suggestion, was that
we end up with too many instructions at once.   Though I do agree that M and MR
are important, and not unrelated.

Both M and MR multiply two 32 bit numbers with a 64 bit product.

Both D and DR divide a 64 bit number by a 32 bit number with 32 bit quotient
and 32 bit remainder.  It is the 64 bit dividend that suggests SRDA.

A 32 bit dividend is loaded into the even register of an even-odd pair, and
then shifted right 32 bits.  This sign extends it, so that D or DR can be
used.  If the number is known positive, then you can just clear the even
register.  

MH is from the 360 instruction set, but MHI is much newer than that.

-- glen



Fri, 19 Jan 2001 03:00:00 GMT  
 Proposed D & DR instructions of the week
I have to admit I forgot about SRDA being used as a sign extender,
despite the fact it makes slow even slower.  I thought of SRDA being
used for scaling adjustment after a multiply.

In that regard, I don't know if it is worth writing a sample program,
at least for multiply and divide.  There really is not all that much meat
that can be extracted from the instructions themselves.  The only other
meat that could be added is showing how to do scaling with fractional
fixed point numbers, and that is used so infrequently as to be nearly
meaningless.

Now using symbolic scaling with decimal divide can be useful.  The way the
hardware splits the number on a divide is rather wierd...


[snip]

Quote:

>The reason I didn't include M and MR in the original suggestion, was that
>we end up with too many instructions at once.   Though I do agree that M and MR
>are important, and not unrelated.

>Both M and MR multiply two 32 bit numbers with a 64 bit product.

>Both D and DR divide a 64 bit number by a 32 bit number with 32 bit quotient
>and 32 bit remainder.  It is the 64 bit dividend that suggests SRDA.

>A 32 bit dividend is loaded into the even register of an even-odd pair, and
>then shifted right 32 bits.  This sign extends it, so that D or DR can be
>used.  If the number is known positive, then you can just clear the even
>register.  

>MH is from the 360 instruction set, but MHI is much newer than that.

>-- glen

-- Steve Myers

The E-mail addresses in this message are private property.  Any use of them
to  send  unsolicited  E-mail  messages  of  a  commerical  nature  will be
considered trespassing,  and the originator of the message will be  sued in
small claims court in Camden County,  New Jersey,  for the  maximum penalty
allowed by law.



Fri, 19 Jan 2001 03:00:00 GMT  
 
 [ 5 post ] 

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