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62 lines
3.2 KiB
Plaintext
62 lines
3.2 KiB
Plaintext
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/* $DOC$
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$NAME$
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StrDiff()
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$CATEGORY$
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CT3 string functions
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$ONELINER$
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Evaluate the "Edit (Levensthein) Distance" of two strings
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$SYNTAX$
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StrDiff( <cString1>, <cString2>, [<nReplacementPenalty>], [<nDeletionPenalty>],
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[<nInsertionPenalty>] ) -> <nDistance>
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$ARGUMENTS$
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<cString1> string at the "starting point" of the transformation process, default is ""
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<cString2> string at the "end point" of the transformation process, default is ""
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<nReplacementPenalty> penalty points for a replacement of one character, default is 3
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<nDeletionPenalty> penalty points for a deletion of one character, default is 6
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<nInsertionPenalty> penalty points for an insertion of one character, default is 1
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$RETURNS$
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<nDistance> penalty point sum of all operations needed to transform <cString1> to <cString2>
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$DESCRIPTION$
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The StrDiff() functions calculates the so called "Edit" or "Levensthein" distance of two strings.
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This distance is a measure for the number of single character replace/insert/delete operations (so called
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"point mutations") required to transform <cString1> into <cString2> and its value will be the smallest sum of
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the penalty points of the required operations.
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Be aware that this function is both quite time - O(Len(cString1)*Len(cString2)) - and memory consuming -
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O((Len(cString1)+1)*(Len(cString2)+1)*sizeof(int)) - so keep the strings as short as possible.
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E.g., on common 32 bit systems (sizeof(int) == 4), calling StrDiff() with two strings of 1024 bytes
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in length will consume 4 MB of memory. To not impose unneeded restrictions, the function will only check if
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(Len(cString1)+1)*(Len(cString2)+1)*sizeof(int) <= UINT_MAX, although allocing UINT_MAX bytes will not
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work on most systems. If this simple check fails, -1 is returned.
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Also, be aware that there can be an overflow when the penalty points are summed up: Assuming that the
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number of transformation operations is in the order of Max(Len(cString1),Len(cString2)), the penalty point
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sum, that is internally stored in an "int" variable, is in the order of
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(Max(Len(cString1),Len(cString2))*Max(nReplacementPenalty,nDeletionPenalty,nInsertionPentaly).
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The StrDiff() does not do an overflow check due to time performance reasons. Future versions of StrDiff()
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could use a type different to "int" to store the penalty point sum to save memory or to avoid overflows.
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The function is aware of the settings done by SetAtLike(), that means that the wildchar character
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is considered equal to ALL characters.
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$EXAMPLES$
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? StrDiff( "ABC", "ADC" ) // 3, one character replaced
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? StrDiff( "ABC", "AEC" ) // 3, dito
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? StrDiff( "CBA", "ABC" ) // 6, two characters replaced
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? StrDiff( "ABC", "AXBC" ) // 1, one character inserted
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? StrDiff( "AXBC", "ABC" ) // 6, one character removed
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? StrDiff( "AXBC", "ADC" ) // 9, one character removed and one replaced
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$STATUS$
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Ready
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$COMPLIANCE$
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StrDiff() is compatible with CT3's StrDiff().
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$PLATFORMS$
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All
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$FILES$
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Library is hbct.
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$SEEALSO$
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SetAtLike()
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$END$
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*/
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