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package org.eclipse.jgit.diff;
Equivalence function for a Sequence compared by difference algorithm.
Difference algorithms can use a comparator to compare portions of two
sequences and discover the minimal edits required to transform from one
sequence to the other sequence.
Indexes within a sequence are zero-based.
Type parameters: - <S> –
type of sequence the comparator supports.
/**
* Equivalence function for a {@link org.eclipse.jgit.diff.Sequence} compared by
* difference algorithm.
* <p>
* Difference algorithms can use a comparator to compare portions of two
* sequences and discover the minimal edits required to transform from one
* sequence to the other sequence.
* <p>
* Indexes within a sequence are zero-based.
*
* @param <S>
* type of sequence the comparator supports.
*/
public abstract class SequenceComparator<S extends Sequence> {
Compare two items to determine if they are equivalent. It is permissible to compare sequence a with itself (by passing a again in position b). Params: - a –
the first sequence.
- ai – item of
ai to compare. - b –
the second sequence.
- bi – item of
bi to compare.
Returns: true if the two items are identical according to this function's
equivalence rule.
/**
* Compare two items to determine if they are equivalent.
*
* It is permissible to compare sequence {@code a} with itself (by passing
* {@code a} again in position {@code b}).
*
* @param a
* the first sequence.
* @param ai
* item of {@code ai} to compare.
* @param b
* the second sequence.
* @param bi
* item of {@code bi} to compare.
* @return true if the two items are identical according to this function's
* equivalence rule.
*/
public abstract boolean equals(S a, int ai, S b, int bi);
Get a hash value for an item in a sequence. If two items are equal according to this comparator's equals(Sequence, int, Sequence, int) method, then this hash method must produce the same integer result for both items. It is not required for two items to have different hash values if they are unequal according to the equals() method. Params: - seq –
the sequence.
- ptr –
the item to obtain the hash for.
Returns: hash the hash value.
/**
* Get a hash value for an item in a sequence.
*
* If two items are equal according to this comparator's
* {@link #equals(Sequence, int, Sequence, int)} method, then this hash
* method must produce the same integer result for both items.
*
* It is not required for two items to have different hash values if they
* are unequal according to the {@code equals()} method.
*
* @param seq
* the sequence.
* @param ptr
* the item to obtain the hash for.
* @return hash the hash value.
*/
public abstract int hash(S seq, int ptr);
Modify the edit to remove common leading and trailing items. The supplied edit e is reduced in size by moving the beginning A and B points so the edit does not cover any items that are in common between the two sequences. The ending A and B points are also shifted to remove common items from the end of the region. Params: - a –
the first sequence.
- b –
the second sequence.
- e –
the edit to start with and update.
Returns: e if it was updated in-place, otherwise a new edit containing the reduced region.
/**
* Modify the edit to remove common leading and trailing items.
*
* The supplied edit {@code e} is reduced in size by moving the beginning A
* and B points so the edit does not cover any items that are in common
* between the two sequences. The ending A and B points are also shifted to
* remove common items from the end of the region.
*
* @param a
* the first sequence.
* @param b
* the second sequence.
* @param e
* the edit to start with and update.
* @return {@code e} if it was updated in-place, otherwise a new edit
* containing the reduced region.
*/
public Edit reduceCommonStartEnd(S a, S b, Edit e) {
// Skip over items that are common at the start.
//
while (e.beginA < e.endA && e.beginB < e.endB
&& equals(a, e.beginA, b, e.beginB)) {
e.beginA++;
e.beginB++;
}
// Skip over items that are common at the end.
//
while (e.beginA < e.endA && e.beginB < e.endB
&& equals(a, e.endA - 1, b, e.endB - 1)) {
e.endA--;
e.endB--;
}
return e;
}
}