Generally speaking to perform "mathematical" proofs, you need to express
your functions in mathematical language.
If you can do that, then yes, there are ways to "prove" equivalence. But
the code you show is string processing, and I'm not up on my math
representations. That might border on Matrix Algerbra - oh the joys of
eigenvalues, eigenvectors, and eigenspace.
But unless there's some specific project requirement to provide such a
proof (don't laugh, some Gov work I've done would require it), you could
just do a fairly exhaustive test (as someone else mentioned).
For example, you could set something up like this:
------------------------------------------------------
FUNCTION CompareStripFuncs
*-- assumes you have your StripCharsNew and StripCharsOld already defined,
*-- and that cValidChars has been defined
*-- build a cursor of string values you want to check. E.g. if you
archived/logged
*-- the old values that "failed" in some table/file somewhere
CREATE CURSOR curResultCompare (checked_string C(100), result_old C(100),
result_new C(100))
*-- curValues2Check is the cursor that has all the strings that you want to
check - I'll assume the
*-- name of the field that holds the string is cBadCharString
SELECT curValues2Check
SCAN
INSERT INTO curResultCompare ;
(cChecked_string, ;
cRresult_old, ;
cRresult_new) ;
VALUES ;
(cBadCharString, ;
StripCharsOld(cBadCharString, cValidChars), ;
StripCharsNew(cBadCharString, cValidChars))
ENDSCAN
SELECT COUNT(*) as num_not_match FROM cResultCompare ;
WHERE cResult_old <> cResult_new ;
INTO CURSOR curNumFailed NOFILTER
m.nReturnNonMatch = curNumFailed.num_not_match
*-- Or you could pull the actual values that didn't compare right, BROWSE
it, REPORT it, etc.
USE IN (SELECT('curResultCompare'))
USE IN (SELECT('curNumFailed'))
RETURN m.nReturnNonMatch
------------------------------------------------------
If you don't have a set of strings from past events, you could write up a
program to generate a few million variations, interspersing bad character
values in various positions. Note, you could probably reduce the required
number of bad char positions to 1st, last, and randomly in middle (and
cases where all characters are bad). If you need to document the results
(aka for a project requirement) you could "check in" the test data and a
report of the results. If you just need it for your peace of mind, you can
be satisfied when you see they gave the same result.
-Charlie
At 07:02 PM 7/17/2009 +0300, Paul Newton wrote:
>Hi
>
>Is it ever possible to prove, scientifically or mathematically, that two
>functions are exactly equivalent ?
>For example, these two functions:
>
>Function StripCharsNew(tcInvalidValue, tcValidCharSet)
>Local lcValidValue, lnCharNo
>lcValidValue = tcInvalidValue
>For lnCharNo = 1 to Len(tcInvalidValue)
> If At(Substr(tcInvalidValue, lnCharNo, 1), tcValidCharSet) = 0
> lcValidValue =
> ChrTran(lcValidValue,Substr(tcInvalidValue, lnCharNo, 1),tcReplaceChar)
> EndIf
>Next
>Return lcValidValue
>EndFunc
>
>Function StripCharsOld(tcInvalidValue, tcValidCharSet)
>Local lcValidValue, lnCharNo
>lcValidValue = ""
>For lnCharNo = 1 to Len(tcInvalidValue)
> If At(Substr(tcInvalidValue, lnCharNo, 1), tcValidCharSet) > 0
> lcValidValue = lcValidValue + Substr(tcInvalidValue,
> lnCharNo, 1)
> EndIf
>Next
>Return lcValidValue
>EndFunc
>
>Thanks
>
>Paul Newton
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