Path: utzoo!utgpu!news-server.csri.toronto.edu!torsqnt!hybrid!torag!utdoe!generic!pnet91!ericmcg
From: ericmcg@pnet91.cts.com (Eric Mcgillicuddy)
Newsgroups: comp.sys.apple2
Subject: Re: help optimizing asm routine (and help with GetCaretTime)
Message-ID: <769@generic.UUCP>
Date: 25 May 91 07:15:06 GMT
Sender: root@generic.UUCP
Organization: People-Net [pnet91], Etobicoke, ON
Lines: 24

Do you want them optimized for speed or memory? Both right?

Anyhow, the scroll_offscreen_grafport can be sped up considerably by using the
MVP instruction. This is off the top of my head and untested, so.....

:6      lda     #num_bytes_2_move-1     ;159?
        _set_8_bit registers_XY         
        ldx     offimage+2              ;zero page variable
        sta     move+1
        ldx     immage+2
        stx     move+2                  ;self modifying code (note stx move+1)
        _set_16_bit_registers_XY
        ldx     offimage                ;holds address of LAST byte to move
        ldy     image                   ;holds address of LAST byt of
        mvp     #0,#0                   ;destination - #0,#0 are dummy numbers

That should do the copy much faster, 7 cycles per byte rather than 14 cycles
per byte. A limitation is that the source and destination not cross banks. Use
the same code with MVN to scroll DOWN. (or vice versa, it's late right now)

Hope this is useful.

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