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SnTT: Performance considerations for Instr

by Bernd,
assono GmbH, Standort Hamburg,

Show-n-Tell Thursday I had to learn the hard way that are big differences in using the LotusScript function Instr case-sensitiv or case-insensitiv. With big differences I mean something like 900 times slower using the option "case-insensitive, pitch-insensitive".

If the text to search is small you won't hardly recognize any difference at all. But if the text is getting bigger you might feel the difference. For the example where I measured a 900 time slower execution time I used a quite long "Lorem ipsum" text (5539 chars) which I concatenated ten times. For the measurement I used a profiling routine from Thomas Bahn.

For i = 1 To 10
text = text & CRLF & text

For i = 1 To 1000
Call StartProfiling("InstrTest", "case-sensitiv")
pos = Instr(text, "Defacto")
Call StopProfiling("InstrTest", "case-sensitiv")

For i = 1 To 1000
Call StartProfiling("InstrTest", "case-insensitiv")
pos = Instr(1, text, "Defacto",5)
Call StopProfiling("InstrTest", "case-insensitiv")

Call LogProfiles()

The results are quite astonishing.

Option Calls Execution time
Execution time
case-insensitiv 1000 459,640 0,45964
case-sensitiv 1000 0,063 0,00006

In my application I needed the case-insensitiv
method to ensure that I found all entries. It is a quite common approach
to gain performance by using more memory. I used a second variable in which
the text was stored converted to lower case. To find the position I just
used the second variable.

i = 1 To 1000

StartProfiling("InstrTest", "case-sensitiv mit Lcase")

textSmallLetters = Lcase(text)

pos =
Instr(textSmallLetters, Lcase("Defacto"))

StopProfiling("InstrTest", "case-sensitiv mit Lcase")


The performance gain with this approach
was quite good. It is not as fast as using the case-sensitiv option. But
for my application it was good enough.

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