Re: lookups and performance -- RPG400-L

Mail List wrote:

Hi Rick,

FWIW, %lookup has a 4th parm -- number of elements to search.  In other
words, load 100 elements of a 1000-element array and do

x = %lookup(SearchFor: Array: StartElem: #ElemToSearch)

With a binary search, I'm not sure there'd be a significant increase in
performance.
...

----- Original Message -----
From: "Richard B Baird"

is there an appreciable difference between that and back filling my array
with hivals and starting at the beginning?

for example (on a much smaller scale - my array is set at 9999 with a
possibility of more than a 1000 valid iters, in otherwords, about 1/10th
full.

Peter is correct. The binary search is an O(log2(n)) algorithm, which roughly means that you have to search through a much bigger set of data to get an appreciable difference in search time. Roughly, it takes 10 iterations to search through an array of about 1000 items. For an array of 1,000,000 items, the algorithm iterates 20 times. So an array 1000 times bigger can be searched in only twice the time.

Yes, if you want significant performance improvements, do look elsewhere. Good profiling tools are essential in identifying the bottlenecks and in verifying that any change does indeed improve performance. The latter point is important since often changes made in the name of performance can be counter-intuitive.

Cheers! Hans

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