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Re: Solving the Floating-Point Goldilocks Problem!

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On 9/5/2011 7:41 AM, Rob Warnock wrote:
> Peter Flass<Peter_Flass@Yahoo.com>  wrote:
> +---------------
> | jmfbahciv wrote:
> |>  <snort>    I don't consider our byte instructions CISCy.  My opinion,
> |>  which has to be taken as an uneducated opinion in c.a, is that
> |>  the PDP-10 had the RISC philosophy underneath.
> |
> | I'd not say they were CISCy.  As I recall there was ILDB and IDPB for
> | byte loads and stores that were register-storage; no storage to storage
> | stuff.  The comp.arch people know a lot more about the details than I do,
> | but a barrel-shifter and a few gates for masking would be all you'd need.
> +---------------
>
> I suspect you may be confusing [or misremembering] two independent
> aspects of the PDP-10:
>
> 1. The byte pointer instructions, LDB/ILDB/DPB/IDPB/IBP, were "memory-
>     reference" instructions, and thus worked on byte pointers which were
>     located *in memory*: the instructions used the normal address resolution
>     (including indexing&  indirection) to get to the byte pointers.
>     The byte pointers themselves also accessed the data they referenced
>     *in memory* (and also including potential indexing&  indirection).
>
> 2. The 16 general purpose accumulators -- a.k.a. registers -- were also
>     accessible *as memory* by any memory-reference instruction, at memory
>     locations 0-15 [0-17 octal]. [In the first PDP-6, they *were* actually
>     memory -- the "fast registers" were a later, high-priced option.]
>
>     Now on the KA-10 [which had no cache(!), but on which the "fast
>     register" option was standard (IIRC)] putting little bits of code
>     or byte pointers or data accessed by byte pointers into the registers
>     and jumping to them (for code, or using memory-reference instructions,
>     for data) was significantly faster than putting then in memory, since
>     the registers were fast TTL (4x4?) register files whereas the core
>     memory cycle times were 1.0us, 1.67us, or slower, depending on the
>     model of core. So "clever" programs often put the inner loops of
>     searches (or whatever) into the regs... or byte pointers, or data
>     that needed to be munged multiple times.
>
>     Unfortunately, by the time the KL-10 came out, the interactions
>     with instruction fetching, the MMU delays, and caching made using
>     the registers as "memory" actually *slower* than putting the code/data
>     in real memory.
>
>     [I don't remember whether on the intermediate KI-10 it was faster
>     or slower to do so. Barb?]
>
> So while you *could* put byte pointer instructions, or byte pointers,
> or the data they referenced into registers, that was *not* required
> [and wasn't even fastest, on the later machiens].
>

Thanks Rob, yes, it was long ago and far away, so I've probaby forgotten 
more about the PDP-10 than I ever knew;-)

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Re: Solving the Floating-Point Goldilocks Problem! jmfbahciv <See.above@aol.com> - 2011-09-01 13:39 +0000
  Re: Solving the Floating-Point Goldilocks Problem! "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-09-01 08:18 -0700
    Re: Solving the Floating-Point Goldilocks Problem! jmfbahciv <See.above@aol.com> - 2011-09-02 13:44 +0000
      Re: Solving the Floating-Point Goldilocks Problem! "Andy \"Krazy\" Glew" <andy@SPAM.comp-arch.net> - 2011-09-02 09:37 -0700
        Re: Solving the Floating-Point Goldilocks Problem! Patrick Scheible <kkt@zipcon.net> - 2011-09-02 10:21 -0700
          Re: Solving the Floating-Point Goldilocks Problem! rpw3@rpw3.org (Rob Warnock) - 2011-09-05 06:11 -0500
        Re: Solving the Floating-Point Goldilocks Problem! jmfbahciv <See.above@aol.com> - 2011-09-03 14:57 +0000
          Re: Solving the Floating-Point Goldilocks Problem! Peter Flass <Peter_Flass@Yahoo.com> - 2011-09-03 13:13 -0400
            Re: Solving the Floating-Point Goldilocks Problem! rpw3@rpw3.org (Rob Warnock) - 2011-09-05 06:41 -0500
              Re: Solving the Floating-Point Goldilocks Problem! Peter Flass <Peter_Flass@Yahoo.com> - 2011-09-05 08:21 -0400
              Re: Solving the Floating-Point Goldilocks Problem! jmfbahciv <See.above@aol.com> - 2011-09-05 13:26 +0000
            Re: Solving the Floating-Point Goldilocks Problem! Patrick Scheible <kkt@zipcon.net> - 2011-09-05 22:48 -0700
              Re: Solving the Floating-Point Goldilocks Problem! Quadibloc <jsavard@ecn.ab.ca> - 2011-09-06 16:51 -0700
                Re: Solving the Floating-Point Goldilocks Problem! Morten Reistad <first@last.name> - 2011-09-07 14:14 +0200
                Re: Solving the Floating-Point Goldilocks Problem! Patrick Scheible <kkt@zipcon.net> - 2011-09-07 09:45 -0700
                Re: Solving the Floating-Point Goldilocks Problem! Rob Doyle <radioengr@gmail.com> - 2011-09-07 18:54 -0700
                Re: Solving the Floating-Point Goldilocks Problem! Quadibloc <jsavard@ecn.ab.ca> - 2011-09-08 00:53 -0700
                Re: Solving the Floating-Point Goldilocks Problem! MitchAlsup <MitchAlsup@aol.com> - 2011-09-08 08:00 -0700

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