/** {@inheritDoc} */
@Override
protected List<SearchResult<SequenceMatcher>> doSearchBackwards(
final WindowReader reader, final long fromPosition, final long toPosition)
throws IOException {
// Initialise:
final SearchInfo info = backwardInfo.get();
final int[] safeShifts = info.shifts;
final ByteMatcher startOfSequence = info.matcher;
final SequenceMatcher verifier = info.verifier;
long searchPosition = fromPosition;
// Search backwards across the windows:
Window window;
while (searchPosition >= toPosition && (window = reader.getWindow(searchPosition)) != null) {
// Initialise the window search:
final byte[] array = window.getArray();
final int arrayStartPosition = reader.getWindowOffset(searchPosition);
final long distanceToEnd = toPosition - window.getWindowPosition();
final int lastSearchPosition = distanceToEnd > 0 ? (int) distanceToEnd : 0;
int arraySearchPosition = arrayStartPosition;
// Search using the byte array for shifts, using the WindowReader
// for verifiying the sequence with the matcher:
ARRAY_SEARCH:
while (arraySearchPosition >= lastSearchPosition) {
// Shift backwards until we match the first position in the sequence,
// or we run out of search space.
byte currentByte = array[arraySearchPosition];
while (!startOfSequence.matches(currentByte)) {
arraySearchPosition -= safeShifts[currentByte & 0xff];
if (arraySearchPosition < lastSearchPosition) {
break ARRAY_SEARCH;
}
currentByte = array[arraySearchPosition];
}
// The first byte matched - verify there is a complete match.
final int totalShift = arrayStartPosition - arraySearchPosition;
final long sequencePosition = searchPosition - totalShift;
if (verifier == null || verifier.matches(reader, sequencePosition + 1)) {
return SearchUtils.singleResult(sequencePosition, matcher); // match found.
}
// No match was found - shift backward by the shift for the current byte:
arraySearchPosition -= safeShifts[currentByte & 0xff];
}
// No match was found in this array - calculate the current search position:
searchPosition -= (arrayStartPosition - arraySearchPosition);
}
return SearchUtils.noResults();
}
/**
* Searches forward using the Boyer Moore Horspool algorithm, using byte arrays from Windows to
* handle shifting, and the WindowReader interface on the SequenceMatcher to verify whether a
* match exists.
*/
@Override
protected List<SearchResult<SequenceMatcher>> doSearchForwards(
final WindowReader reader, final long fromPosition, final long toPosition)
throws IOException {
// Get the objects needed to search:
final SearchInfo info = forwardInfo.get();
final int[] safeShifts = info.shifts;
final ByteMatcher endOfSequence = info.matcher;
final SequenceMatcher verifier = info.verifier;
// Initialise window search:
final long endSequencePosition = matcher.length() - 1;
final long finalPosition = toPosition + endSequencePosition;
long searchPosition = fromPosition + endSequencePosition;
// While there is a window to search in:
Window window;
while (searchPosition <= finalPosition && (window = reader.getWindow(searchPosition)) != null) {
// Initialise array search:
final byte[] array = window.getArray();
final int arrayStartPosition = reader.getWindowOffset(searchPosition);
final int arrayEndPosition = window.length() - 1;
final int lastMatcherPosition = matcher.length() - 1;
final long distanceToEnd = finalPosition - window.getWindowPosition() + lastMatcherPosition;
final int lastSearchPosition =
distanceToEnd < arrayEndPosition ? (int) distanceToEnd : arrayEndPosition;
int arraySearchPosition = arrayStartPosition;
// Search forwards in this array:
ARRAY_SEARCH:
while (arraySearchPosition <= lastSearchPosition) {
// Shift forwards until we match the last position in the sequence,
// or we run out of search space.
byte currentByte = array[arraySearchPosition];
while (!endOfSequence.matches(currentByte)) {
arraySearchPosition += safeShifts[currentByte & 0xff];
if (arraySearchPosition > lastSearchPosition) {
break ARRAY_SEARCH; // outside the array, move on.
}
currentByte = array[arraySearchPosition];
}
// The last byte matched - verify there is a complete match:
final long arrayBytesSearched = arraySearchPosition - arrayStartPosition;
final long matchPosition = searchPosition + arrayBytesSearched - endSequencePosition;
if (verifier.matches(reader, matchPosition)) {
return SearchUtils.singleResult(matchPosition, matcher); // match found.
}
// No match was found - shift forward by the shift for the current byte:
arraySearchPosition += safeShifts[currentByte & 0xff];
}
// No match was found in this array - calculate the current search position:
searchPosition += arraySearchPosition - arrayStartPosition;
}
return SearchUtils.noResults();
}