Repeat loop index

[Mark Brownell]

On Monday, July 14, 2003, at 03:23  PM, Richard Gaskin wrote:

> Actually, that won't work: "repeat for each" requires you to specify a 
> chunk
> variable, like this:
>
>  repeat for each line tMyLine of tText
>    doSomething(tMyLine)
>  end repeat
>
> Why is it so much faster?
>
> When you say:
>
>    get line i of tText
>
> ...it has to walk through all the characters from the beginning, 
> counting
> carriage returns as it goes, until it reaches i number of lines.   This
> creates a scaling problem:  the first time through the loop it's pretty
> fast, but by the end it could be traversing hundreds or thousands of 
> lines
> each time through.  It does this with the most flexible assumption: if
> something in the loop changes tText, only this brute-force method will
> accurately count lines.
>
> The "repeat for each" form works on a different assumption:  in cases 
> where
> you know tText won't change during the loop, the engine can afford to 
> keep a
> pointer into tText that tells it where it left off.  Each time through 
> the
> loop it only counts forward from where it last left off to the end of 
> the
> next line, so it scales beautifully:  each iteration takes almost 
> exactly
> the same time as the last.
>
> And with specifying a chunk variable in the repeat statement, the 
> chunk is
> already parsed and stored in that var each iteration, ready for use.
>
> -- 
>  Richard Gaskin

Well I'll be. This might actually optimize RevBlowfish.

This:

   put 1 into ic
   put 1 into ix
   repeat while ic <= textCryptLength
     put char ix to (ix + 3) of cryptThisText into strXL
     put char (ix + 4) to (ix + 7)  of cryptThisText into strXL

might works as:

repeat for each char tMychunk of cryptThisText  step 8
     put char 1 to 4 of tMychunk into strXL
     put char 5 to 8 of tMychunk into strXR

Does anyone know if "repeat for each char" works with step?

Mark

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