Speeding up code: Removing invariants from loops.

[ChrisGreaves]

I don't know what I was thinking; for years I've been telling folks to take invariant calculations out of loops.
OLD:

Code: Select all

For Each strP In rng.Paragraphs
    Call strStatusBar("Loading " & Format(100 * (strP.Range.Start / ActiveDocument.Characters.Count), "##0.000") & "%")

NEW:

Code: Select all

Dim lngCharCount As Long
lngCharCount = ActiveDocument.Characters.Count
For Each strP In rng.Paragraphs
    Call strStatusBar("Loading " & Format(100 * (strP.Range.Start / lngCharCount), "##0") & "%")

Compare the two chunks of code above; I've been waiting for up to two minutes each shot to get statistics on a 20,000 word essay.
The new code flashes by so quickly I almost don't get time to read the formatted string in the Statusbar!
I stared at the 3-decimal places in the Statusbar string, decided to get rid of them by changing the format string, and found the call to ActiveDocument.Characters.Count right there inside the loop.
That has prompted me to search my code database looking for all other occurences of ActiveDocument.Characters. and similar constructs.

[agibsonsw]

I'm confused. lngCharCount will be an invariant so how can Characters.Count appear within the (2nd) loop?

[HansV]

Assuming that you don't modify the document within the loop, the character count (which has been calculated just before the loop and stored in lngCharCount) will remain the same, so it's legitimate to use lngCharCount within the loop.