Inefficient code - Solutions

[BNig]

Bill,

Bill Marriott wrote:
> 
> Can anyone improve on it?
> 

well, only Bill can. I used your logic and added a forward search when the
comparison is not unequal, figuring that going forward yields faster
results. Well it kind of does, if one thinks 5 to 10 milliseconds are an
improvement... 
I would not have posted it if you hadn't asked.

the change is marked in the code.
this code is working code in Bill's stack.

-------------------------------------------
on mouseUp
   put the imagedata of image "Alpha" of group (the activeTab of btn "Image
Style") into ImageA
   put the imagedata of image "Beta" of group (the activeTab of btn "Image
Style") into ImageB
   set the endvalue of scrollbar "Progress" to \
          the length of imagedata of image "Alpha" of group (the activeTab
of btn "Image Style")
   
   put 0 into currPixel
   put the length of ImageA into dataLength
   put dataLength into rangeToCheck
   put 4 into tIncrement
   put the milliseconds into t
   -- begin timing
   repeat while currPixel < dataLength
      -- starting with the whole image, check a range of pixels for
differences
      -- keep slicing the range in half until we find a block of unchanged
pixels
      repeat while char currPixel+1 to currPixel+rangeToCheck of ImageA <> \
             char currPixel+1 to currPixel+rangeToCheck of ImageB
         -- aha, the range we're testing has changes
         if rangeToCheck >= 8 then
            --breakpoint
            -- eight bytes is at least two pixels... it's still too big;
slice it in half
            put rangeToCheck div 4 div 2 * 4 into rangeToCheck
         else
            -- we're down to a single changed pixel now
            -- record which pixel has changed (offset within the imageData)
            put 1 into bytesChanged[currPixel+1]
            -- move to the next pixel; assume that changed pixels are near
each other
            add 4 to currPixel
         end if
      end repeat
      -- we found one or more unchanged pixels; skip this section of data
      add rangeToCheck to currPixel
      
      -- this is added to Bill's original code
      -- assume there are more unchanged pixels and go forwards
      repeat while char currPixel+1 to currPixel+tIncrement of ImageA = \
             char currPixel+1 to currPixel+tIncrement of ImageB
         add tIncrement to currPixel
         add tIncrement to tIncrement
         if tIncrement > dataLength then exit repeat
      end repeat
      -- end addition to Bill's code
      
      -- and update the range to encompass the remainder of the image
      put dataLength - currPixel into rangeToCheck
   end repeat
   
   -- end timing
   put the milliseconds - t into d
   put the keys of bytesChanged into t
   sort t numeric
   put t into field "diff"
   set the thumbposition of scrollbar "Progress" to the endValue of
scrollbar "Progress"
   put the number of lines in fld "Diff" && "pixels changed," && d &&
"milliseconds"
end mouseUp
------------------------------------------
as usual, watch out for linebreaks

regards
Bernd

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