/**
* 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);
}
/** {@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();
}
/** {@inheritDoc} */
@Override
public List<SearchResult<SequenceMatcher>> searchForwards(
final byte[] bytes, final int fromPosition, final int toPosition) {
// 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;
// Determine a safe position to start searching at.
final int lastMatcherPosition = getMatcher().length() - 1;
int searchPosition =
fromPosition > 0 ? fromPosition + lastMatcherPosition : lastMatcherPosition;
// Calculate safe bounds for the end of the search:
final int lastPossiblePosition = bytes.length - 1;
final int lastPossibleSearchPosition = toPosition + lastMatcherPosition;
final int finalPosition =
lastPossibleSearchPosition < lastPossiblePosition
? lastPossibleSearchPosition
: lastPossiblePosition;
// Search forwards:
while (searchPosition <= finalPosition) {
// Shift forwards until we match the last position in the sequence,
// or we run out of search space (in which case just return not found).
byte currentByte = bytes[searchPosition];
while (!endOfSequence.matches(currentByte)) {
searchPosition += safeShifts[currentByte & 0xff];
if (searchPosition > finalPosition) {
return SearchUtils.noResults();
}
currentByte = bytes[searchPosition];
}
// The last byte matched - verify there is a complete match:
final int startMatchPosition = searchPosition - lastMatcherPosition;
if (verifier.matchesNoBoundsCheck(bytes, startMatchPosition)) {
return SearchUtils.singleResult(startMatchPosition, matcher); // match found.
}
// No match was found - shift forward by the shift for the current byte:
searchPosition += safeShifts[currentByte & 0xff];
}
return SearchUtils.noResults();
}
/** {@inheritDoc} */
@Override
public List<SearchResult<SequenceMatcher>> searchBackwards(
final byte[] bytes, final int fromPosition, final int toPosition) {
// Get objects needed for the search:
final SearchInfo info = backwardInfo.get();
final int[] safeShifts = info.shifts;
final ByteMatcher startOfSequence = info.matcher;
final SequenceMatcher verifier = info.verifier;
// Calculate safe bounds for the start of the search:
final int firstPossiblePosition = bytes.length - getMatcher().length();
int searchPosition =
fromPosition < firstPossiblePosition ? fromPosition : firstPossiblePosition;
// Calculate safe bounds for the end of the search:
final int lastPosition = toPosition > 0 ? toPosition : 0;
// Search backwards:
while (searchPosition >= lastPosition) {
// Shift backwards until we match the first position in the
// sequence, or we run out of search space:
byte currentByte = bytes[searchPosition];
while (!startOfSequence.matches(currentByte)) {
searchPosition -= safeShifts[currentByte & 0xFF];
if (searchPosition < lastPosition) {
return SearchUtils.noResults();
}
currentByte = bytes[searchPosition];
}
// The first byte matched - verify there is a complete match.
// There is only a verifier if the sequence length was greater than one;
// if the sequence is only one in length, we have already found it.
if (verifier == null || verifier.matchesNoBoundsCheck(bytes, searchPosition + 1)) {
return SearchUtils.singleResult(searchPosition, matcher); // match found.
}
// No match was found - shift backward by the shift for the current byte:
searchPosition -= safeShifts[currentByte & 0xff];
}
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();
}
