https://bz.apache.org/bugzilla/show_bug.cgi?id=59773
Bug ID: 59773
Summary: Move loop invariants outside of loop for faster
execution
Product: POI
Version: 3.15-dev
Hardware: Other
OS: All
Status: NEW
Severity: enhancement
Priority: P2
Component: POI Overall
Assignee: [email protected]
Reporter: [email protected]
POI has a fair amount of code that reads
for(int i=0; i<getNumberOfStyles(); i++) {
// do something
}
The call to getNumberOfStyles is called for every loop iteration. At best this
is a lot of function calls. At worst, this is a lot of expensive function
calls.
We can pretty easily find cases where we can make POI faster by moving loop
invariants (value doesn't change over the for loop, function doesn't have any
side-effects) outside the loop.
grep -r --exclude-dir=".svn" -P "for\s*\([^:\(]+\(\)[^:\)]+\)"
This finds function calls within a for loop, excluding for-each loops.
There are currently 514 instances. Some may be for-loops over iterators or
functions with side-effects. The rest could probably be made faster without
harming readability.
There are likely expressions or functions that are re-evaluated with loops that
could be pulled out of an inner loop or loops entirely, but this is a bit
trickier to find with a reg ex.
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