Re: OOS approach revisited

On 27 Jun 2025 at 22:35:32 CEST, "minforth" <minforth@gmx.net> wrote:

Am 27.06.2025 um 20:15 schrieb albert@spenarnc.xs4all.nl:

In article <bc63996456fe967e5c66d17cbbeb21c2@www.novabbs.com>,
LIT <zbigniew2011@gmail.com> wrote:

It really depends on how counted loops are implemented.
Most CPUs have operators for register-based count-down loops
that are blazingly fast.
 
If they can be used within Forth-based loop constructs
I would expect a greater speed increase than what you measured.

 
In that old fig-Forth it's rather short and simple:
 
        sqHeader '(LOOP)'
XLOOP   dw   $ + 2
        mov  BX,1
XLOO1:  add  [BP],BX
        mov  AX,[BP]
        sub  AX,[BP+2]
        xor  AX,BX
        js   BRAN1
        add  BP,4
        inc  SI
        inc  SI
        jmp  NEXT
 
It doesn't look that bad. Can it be
done even shorter?

 
My optimiser looks into the combination of DO and LOOP,
transfers the returns stack into registers after inlining
everything. It is near vfx performance.
All experimental, but yes there is much to be gained.

 
Must be tricky to do UNLOOP in a register-based loop.  ;-)

Here are the code generators for VFX x64 LOOP and UNLOOP.
All the complexity is in the DO and ?DO code.

: c_loop        \ mrk> drbid -- ; compile code for LOOP ; SFP094
  c_shuffle reset-opt            \ SFP097
  a[ INC    r14 ]a  use-a        \ update index
  a[ INC    r15 ]a  use-a        \ update limit-index-$8000.0000
  a[ JNO ]a  <ares  use-a        \ resolve backward branch
  c_unloop                              \ remove DO ... LOOP state
  >RES                                  \ resolve forward branch
;

: c_unloop      \ -- ; compile code for UNLOOP
  c_shuffle  reset-opt
  a[  pop    r14        \ restore old index
      pop    r15        \ restore old index-limit-xorbit63
      pop    rax        \ discarded
  ]a  use-a
;

Stephen
--
Stephen Pelc, stephen@vfxforth.com
Wodni & Pelc GmbH
Vienna, Austria
Tel: +44 (0)7803 903612, +34 649 662 974
http://www.vfxforth.com/downloads/VfxCommunity/
  free VFX Forth downloads