/**
* Calculates the safe shifts to use if searching backwards. A safe shift is either the length
* of the sequence, if the byte does not appear in the {@link SequenceMatcher}, or the shortest
* distance it appears from the beginning of the matcher, with zero being the value of the first
* position in the sequence.
*/
@Override
public SearchInfo create() {
// Get info about the matcher:
final SequenceMatcher sequence = getMatcher();
final int sequenceLength = sequence.length();
// Create the search info object fields
final int lastPosition = sequenceLength - 1;
final ByteMatcher byteMatcher = sequence.getMatcherForPosition(0);
final SequenceMatcher verifier =
(lastPosition == 0) ? null : sequence.subsequence(1, sequenceLength);
// Set the default shift to the length of the sequence
final int[] shifts = new int[256];
Arrays.fill(shifts, sequenceLength);
// Now set specific byte shifts for the bytes actually in
// the sequence itself. The shift is the position in the sequence,
// but we do not create a shift for the first position 0.
for (int sequencePos = lastPosition; sequencePos > 0; sequencePos--) {
final ByteMatcher aMatcher = sequence.getMatcherForPosition(sequencePos);
final byte[] matchingBytes = aMatcher.getMatchingBytes();
for (final byte b : matchingBytes) {
shifts[b & 0xFF] = sequencePos;
}
}
return new SearchInfo(shifts, byteMatcher, verifier);
}
/**
* Calculates the safe shifts to use if searching forwards. A safe shift is either the length of
* the sequence, if the byte does not appear in the {@link SequenceMatcher}, or the shortest
* distance it appears from the end of the matcher.
*/
@Override
public SearchInfo create() {
// Get info about the matcher:
final SequenceMatcher sequence = getMatcher();
final int sequenceLength = sequence.length();
// Create the search info object fields:
final int lastPosition = sequenceLength - 1;
final ByteMatcher byteMatcher = sequence.getMatcherForPosition(lastPosition);
final SequenceMatcher verifier =
(lastPosition == 0)
? AnyByteMatcher.ANY_BYTE_MATCHER
: sequence.subsequence(0, lastPosition);
// Set the default shift to the length of the sequence for all possible byte values:
final int[] shifts = new int[256];
Arrays.fill(shifts, sequenceLength);
// Now set specific shifts for the bytes actually in
// the sequence itself. The shift is the distance of a position
// from the end of the sequence, but we do not create a shift for
// the very last position.
for (int sequencePos = 0; sequencePos < lastPosition; sequencePos++) {
final ByteMatcher aMatcher = sequence.getMatcherForPosition(sequencePos);
final byte[] matchingBytes = aMatcher.getMatchingBytes();
final int distanceFromEnd = sequenceLength - sequencePos - 1;
for (final byte b : matchingBytes) {
shifts[b & 0xFF] = distanceFromEnd;
}
}
return new SearchInfo(shifts, byteMatcher, verifier);
}
