Affects Version/s: None
Fix Version/s: 5.7.0
org.zkoss.poi.ss.formula.eval.OperandResolver.fpRegex will be used for many times when converting a string to a double in a formula.
As Pattern javadoc recommends:
If a pattern is to be used multiple times, compiling it once and reusing it will be more efficient than invoking this method each time.
We should use a compiled one.