Do not reindex files if their contents haven't changed. Bug 302083.

core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/scanner/ScannerTestSuite.java

@@ -25,6 +25,7 @@ public class ScannerTestSuite extends TestSuite {
 		suite.addTest(PreprocessorBugsTests.suite());
 		suite.addTest(ExpansionExplorerTests.suite());
 		suite.addTest(InactiveCodeTests.suite());
+		suite.addTest(StreamHasherTests.suite());
 		return suite;
 	}	
 }

core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/core/parser/tests/scanner/StreamHasherTests.java

@@ -0,0 +1,90 @@
+/*******************************************************************************
+ * Copyright (c) 2010 Google, Inc and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ * 	  Sergey Prigogin (Google) - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.cdt.core.parser.tests.scanner;
+
+import junit.framework.TestSuite;
+
+import org.eclipse.cdt.core.testplugin.util.BaseTestCase;
+import org.eclipse.cdt.internal.core.parser.scanner.StreamHasher;
+
+/**
+ * Unit test for StreamHasher class.
+ */
+public class StreamHasherTests extends BaseTestCase {
+	
+	private static final String TEXT =
+		    "'Twas brillig, and the slithy toves\r\n" +
+			"Did gyre and gimble in the wabe;\r\n" +
+			"All mimsy were the borogoves,\r\n" +
+			"And the mome raths outgrabe.\r\n" +
+			"\r\n" +
+			"\"Beware the Jabberwock, my son!\r\n" +
+			"The jaws that bite, the claws that catch!\r\n" +
+			"Beware the Jubjub bird, and shun\r\n" +
+			"The frumious Bandersnatch!\"\r\n" +
+			"\r\n" +
+			"He took his vorpal sword in hand:\r\n" +
+			"Long time the manxome foe he sought—\r\n" +
+			"So rested he by the Tumtum tree,\r\n" +
+			"And stood awhile in thought.\r\n" +
+			"\r\n" +
+			"And as in uffish thought he stood,\r\n" +
+			"The Jabberwock, with eyes of flame,\r\n" +
+			"Came whiffling through the tulgey wood,\r\n" +
+			"And burbled as it came!\r\n" +
+			"\r\n" +
+			"One, two! One, two! and through and through\r\n" +
+			"The vorpal blade went snicker-snack!\r\n" +
+			"He left it dead, and with its head\r\n" +
+			"He went galumphing back.\r\n" +
+			"\r\n" +
+			"\"And hast thou slain the Jabberwock?\r\n" +
+			"Come to my arms, my beamish boy!\r\n" +
+			"O frabjous day! Callooh! Callay!\"\r\n" +
+			"He chortled in his joy.\r\n" +
+			"\r\n" +
+			"'Twas brillig, and the slithy toves\r\n" +
+			"Did gyre and gimble in the wabe;\r\n" +
+			"All mimsy were the borogoves,\r\n" +
+			"And the mome raths outgrabe.\r\n";
+
+	public static TestSuite suite() {
+		return suite(StreamHasherTests.class);
+	}
+
+	public StreamHasherTests() {
+		super();
+	}
+
+	public StreamHasherTests(String name) {
+		super(name);
+	}
+
+	public void testEmpty() throws Exception {
+		// Verify that an empty string has a zero hash value.
+		assertEquals(0, StreamHasher.hash(""));
+		assertEquals(0, new StreamHasher().computeHash());
+	}
+
+	public void testChunks() throws Exception {
+		// Verify that the hash value does not depend on partitioning of the character string into chunks.
+		long h = StreamHasher.hash(TEXT);
+		assertTrue(h != 0);
+		for (int chunkSize = 1; chunkSize <= 20; chunkSize++) {
+			StreamHasher hasher = new StreamHasher();
+			for (int offset = 0; offset < TEXT.length(); offset += chunkSize) {
+				char[] chunk = TEXT.substring(offset, Math.min(offset + chunkSize, TEXT.length())).toCharArray();
+				hasher.addChunk(chunk);
+			}
+			assertEquals(h, hasher.computeHash());
+		}
+	}
+}

core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/internal/index/tests/IndexListenerTest.java

@@ -91,7 +91,6 @@ public class IndexListenerTest extends BaseTestCase {
 		}
 	}
 		
-
 	public void testChangeListener() throws Exception {
 		final Object mutex= new Object();
 		final List projects= new ArrayList();
@@ -119,8 +118,8 @@ public class IndexListenerTest extends BaseTestCase {
 			projects.clear();
 
 
-			IFile file1= TestSourceReader.createFile(fProject1.getProject(), "test.cpp", "int a;");
+			IFile file1= TestSourceReader.createFile(fProject1.getProject(), "test.cpp", "int b;");
-			IFile file2= TestSourceReader.createFile(fProject2.getProject(), "test.cpp", "int b;");
+			IFile file2= TestSourceReader.createFile(fProject2.getProject(), "test.cpp", "int c;");
 			synchronized (mutex) {
 				mutex.wait(1000);
 				if (projects.size() < 2) {

core/org.eclipse.cdt.core.tests/parser/org/eclipse/cdt/internal/index/tests/IndexUpdateTests.java

@@ -125,7 +125,10 @@ public class IndexUpdateTests extends IndexTestBase {
 	}
 	
 	private void updateFile() throws Exception {
-		fFile= TestSourceReader.createFile(fFile.getParent(), fFile.getName(), fContents[++fContentUsed].toString());
+		// Append variable comment to the end of the file to change its contents.
+		// Indexer would not reindex the file if its contents remain the same. 
+		fFile= TestSourceReader.createFile(fFile.getParent(), fFile.getName(),
+				fContents[++fContentUsed].toString() + "\n// " + fContentUsed); 
 		TestSourceReader.waitUntilFileIsIndexed(fIndex, fFile, INDEXER_WAIT_TIME);
 	}
 	

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/index/IIndexFile.java

@@ -60,6 +60,14 @@ public interface IIndexFile {
 	 */
 	long getTimestamp() throws CoreException;
 
+	/**
+	 * Hash of the file contents when the file was indexed.
+	 * @return 64-bit hash of the file content.
+	 * @throws CoreException
+	 * @since 5.2
+	 */
+	long getContentsHash() throws CoreException;
+
 	/**
 	 * Returns the hash-code of the scanner configuration that was used to parse the file.
 	 * <code>0</code> will be returned in case the hash-code is unknown.

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/index/IIndexManager.java

@@ -79,6 +79,15 @@ public interface IIndexManager extends IPDOMManager {
 	 */
 	public final static int UPDATE_EXTERNAL_FILES_FOR_PROJECT= 0x8;
 
+	/**
+	 * This flag modifies behavior of UPDATE_CHECK_TIMESTAMPS. Both, the timestamp and the hash
+	 * of the contents of a translation unit, have to change in order to trigger re-indexing.
+	 * Checking for content changes may reduce indexing overhead for projects that use code
+	 * generation since generated files are sometimes recreated with identical contents. 
+	 * @since 5.2
+	 */
+	public final static int UPDATE_CHECK_CONTENTS_HASH= 0x10;
+
 	/**
 	 * Returns the index for the given project.
 	 * @param project the project to get the index for
@@ -192,7 +201,7 @@ public interface IIndexManager extends IPDOMManager {
 	 * nested translation units are considered.
 	 * @param tuSelection the translation units to update.
 	 * @param options one of {@link #UPDATE_ALL} or {@link #UPDATE_CHECK_TIMESTAMPS} optionally
-	 * combined with {@link #UPDATE_EXTERNAL_FILES_FOR_PROJECT}.
+	 * combined with {@link #UPDATE_EXTERNAL_FILES_FOR_PROJECT} and {@link #UPDATE_CHECK_CONTENTS_HASH}.
 	 * @throws CoreException
 	 * @since 4.0
 	 */

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/core/parser/FileContent.java

@@ -7,6 +7,7 @@
  *
  * Contributors:
  *    Markus Schorn - initial API and implementation
+ *    Sergey Prigogin (Google)
  *******************************************************************************/ 
 package org.eclipse.cdt.core.parser;
 
@@ -22,8 +23,8 @@ import org.eclipse.core.runtime.IPath;
 
 
 /**
- * Abstract class for representing the content of a file. This serves as the
+ * Abstract class for representing the content of a file.
- * input to the preprocessor.
+ * It serves as the input to the preprocessor.
  *
  * @noextend This class is not intended to be subclassed by clients.
  * @since 5.2
@@ -35,6 +36,10 @@ public abstract class FileContent {
 	 */
 	public abstract String getFileLocation();
 
+	/**
+	 * Returns a 64-bit hash value of the file contents.
+	 */
+	public abstract long getContentsHash();
 
 	/**
 	 * Creates a file content object for a fixed buffer.
@@ -78,7 +83,6 @@ public abstract class FileContent {
 		return InternalParserUtil.createWorkspaceFileContent(file);
 	}
 
-	
 	/**
 	 * Creates a file content object for a file location that is not part of the workspace
 	 */

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/index/IIndexFragmentFile.java

@@ -28,6 +28,11 @@ public interface IIndexFragmentFile extends IIndexFile {
 	 */
 	void setTimestamp(long timestamp) throws CoreException;
 
+	/**
+	 * Sets the hash of the file content. 
+	 */
+	void setContentsHash(long hash) throws CoreException;
+
 	/**
 	 * Sets the hash-code of the scanner configuration.
 	 * @param hashcode a hash-code or <code>0</code> if it is unknown.

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/parser/scanner/AbstractCharArray.java

@@ -7,6 +7,7 @@
  *
  * Contributors:
  *    Markus Schorn - initial API and implementation
+ *    Sergey Prigogin (Google)
  *******************************************************************************/ 
 package org.eclipse.cdt.internal.core.parser.scanner;
 
@@ -35,6 +36,13 @@ public abstract class AbstractCharArray {
 	 */
 	public abstract boolean isValidOffset(int offset);
 
+	/**
+	 * Computes 64-bit hash value of the character array. This method doesn't cause any I/O if called
+	 * after the array has been traversed.
+	 * @return The hash value of the contents of the array.
+	 */
+	public abstract long getContentsHash();
+
 	/**
 	 * Returns the character at the given position, subclasses do not have to do range checks.
 	 */

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/parser/scanner/CharArray.java

@@ -7,16 +7,17 @@
  *
  * Contributors:
  *    Markus Schorn - initial API and implementation
+ *    Sergey Prigogin (Google)
  *******************************************************************************/ 
 package org.eclipse.cdt.internal.core.parser.scanner;
 
-
 /**
  * Wrapper around char[] to implement {@link AbstractCharArray}.
  */
 public final class CharArray extends AbstractCharArray {
 
 	private final char[] fArray;
+	private long hash64;
 
 	public CharArray(char[] array) {
 		fArray= array;
@@ -48,11 +49,20 @@ public final class CharArray extends AbstractCharArray {
 	@Override
 	public void arraycopy(int offset, char[] destination, int destPos, int length) {
 		System.arraycopy(fArray, offset, destination, destPos, length);
-		
 	}
 
 	@Override
 	public boolean isValidOffset(int offset) {
 		return offset < fArray.length;
 	}
+
+	@Override
+	public long getContentsHash() {
+		if (hash64 == 0 && fArray.length != 0) {
+			StreamHasher hasher = new StreamHasher();
+			hasher.addChunk(fArray);
+			hash64 = hasher.computeHash();
+		}
+		return hash64;
+	}
 }

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/parser/scanner/FileCharArray.java

@@ -75,8 +75,6 @@ public class FileCharArray extends LazyCharArray {
 		fCharSet= charSet;
 	}
 
-	
-	
 	@Override
 	protected Chunk createChunk(int chunkOffset) {
 		FileInputStream fis;
@@ -110,7 +108,7 @@ public class FileCharArray extends LazyCharArray {
 		final CharBuffer dest= CharBuffer.allocate(CHUNK_SIZE);
 
 		boolean endOfInput= false;
-		while(dest.position() < CHUNK_SIZE && !endOfInput) {
+		while (dest.position() < CHUNK_SIZE && !endOfInput) {
 			fChannel.position(fileOffset);
 			in.clear();
 			int count= fChannel.read(in);
@@ -127,8 +125,7 @@ public class FileCharArray extends LazyCharArray {
 		dest.flip();
 		return extractChars(dest);
 	}
-	
+
-	
 	@Override
 	protected void rereadChunkData(long fileOffset, long fileEndOffset, char[] dest) {
 		FileInputStream fis;
@@ -156,7 +153,7 @@ public class FileCharArray extends LazyCharArray {
 		final CharsetDecoder decoder = charset.newDecoder().onMalformedInput(CodingErrorAction.REPLACE)
 				.onUnmappableCharacter(CodingErrorAction.REPLACE);
 
-		int needBytes = (int) (fileEndOffset-fileOffset);
+		int needBytes = (int) (fileEndOffset - fileOffset);
 		final ByteBuffer in = ByteBuffer.allocate(needBytes);
 
 		channel.position(fileOffset);

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/parser/scanner/InternalFileContent.java

@@ -7,6 +7,7 @@
  *
  * Contributors:
  *    Markus Schorn - initial API and implementation
+ *    Sergey Prigogin (Google)
  *******************************************************************************/ 
 package org.eclipse.cdt.internal.core.parser.scanner;
 
@@ -115,6 +116,14 @@ public class InternalFileContent extends FileContent {
 		return fFileLocation;
 	}
 
+	/**
+	 * Returns a 64-bit hash value of the file contents.
+	 */
+	@Override
+	public long getContentsHash() {
+		return fSource != null ? fSource.getContentsHash() : 0;
+	}
+
 	/**
 	 * Valid with {@link InclusionKind#USE_SOURCE}.
 	 * @return the codeReader or <code>null</code> if kind is different to {@link InclusionKind#USE_SOURCE}.

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/parser/scanner/LazyCharArray.java

@@ -7,6 +7,7 @@
  *
  * Contributors:
  *    Markus Schorn - initial API and implementation
+ *    Sergey Prigogin (Google)
  *******************************************************************************/ 
 package org.eclipse.cdt.internal.core.parser.scanner;
 
@@ -38,8 +39,11 @@ public abstract class LazyCharArray extends AbstractCharArray {
 	
 	private int fLength= -1;
 	private List<Chunk> fChunks= new ArrayList<Chunk>();
+	private StreamHasher hasher;
+	private long hash64;
 
 	protected LazyCharArray() {
+		hasher = new StreamHasher();
 	}
 
 	@Override
@@ -66,8 +70,18 @@ public abstract class LazyCharArray extends AbstractCharArray {
 		return true;
 	}
 
+	@Override
+	public long getContentsHash() {
+		if (hasher != null) {
+			readUpTo(Integer.MAX_VALUE);
+			hash64 = hasher.computeHash();
+			hasher = null;
+		}
+		return hash64;
+	}
+
 	private void readUpTo(int offset) {
-		if (fLength >=0)
+		if (fLength >= 0)
 			return;
 		
 		final int chunkOffset= offset >> CHUNK_BITS;
@@ -78,13 +92,13 @@ public abstract class LazyCharArray extends AbstractCharArray {
 	public final char get(int offset) {
 		int chunkOffset= offset >> CHUNK_BITS;
 		char[] data= getChunkData(chunkOffset);
-		return data[offset & (CHUNK_SIZE-1)];
+		return data[offset & (CHUNK_SIZE - 1)];
 	}
 
 	@Override
 	public final void arraycopy(int offset, char[] destination, int destinationPos, int length) {
 		int chunkOffset= offset >> CHUNK_BITS;
-		int loffset= offset & (CHUNK_SIZE-1);
+		int loffset= offset & (CHUNK_SIZE - 1);
 		char[] data= getChunkData(chunkOffset);
 		final int canCopy = data.length-loffset;
 		if (length <= canCopy) {
@@ -124,7 +138,7 @@ public abstract class LazyCharArray extends AbstractCharArray {
 	 */
 	protected Chunk createChunk(int chunkOffset) {
 		final int chunkCount = fChunks.size();
-		long fileOffset= chunkCount == 0 ? 0 : fChunks.get(chunkCount-1).fFileEndOffset;
+		long fileOffset= chunkCount == 0 ? 0 : fChunks.get(chunkCount - 1).fFileEndOffset;
 		try {
 			for (int i = chunkCount; i <= chunkOffset; i++) {
 				long[] fileEndOffset= {0};
@@ -133,12 +147,15 @@ public abstract class LazyCharArray extends AbstractCharArray {
 				if (charCount == 0) {
 					fLength= fChunks.size() * CHUNK_SIZE;
 					break;
-				} 
+				}
+				if (hasher != null) {
+					hasher.addChunk(data);
+				}
 				// New chunk
 				Chunk chunk= new Chunk(fileOffset, fileEndOffset[0], data);
 				fChunks.add(chunk);
 				if (charCount < CHUNK_SIZE) {
-					fLength= (fChunks.size()-1) * CHUNK_SIZE + charCount;
+					fLength= (fChunks.size() - 1) * CHUNK_SIZE + charCount;
 					break;
 				} 
 				fileOffset= fileEndOffset[0];
@@ -162,8 +179,8 @@ public abstract class LazyCharArray extends AbstractCharArray {
 	}
 
 	/**
-	 * Read the chunk data at the given source offset and provide the end-offset in the
+	 * Read the chunk data at the given source offset and provide the end-offset in
-	 * source.
+	 * the source.
 	 */
 	protected abstract char[] readChunkData(long sourceOffset, long[] sourceEndOffsetHolder) throws Exception;
 		

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/parser/scanner/StreamHasher.java

@@ -0,0 +1,236 @@
+/*******************************************************************************
+ * Copyright (c) 2010 Google, Inc and others.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ * 	  Sergey Prigogin (Google) - initial API and implementation
+ *
+ * Based on lookup3.c, by Bob Jenkins {@link "http://burtleburtle.net/bob/c/lookup3.c"}
+ *
+ * Here is the original comment by Bob Jenkins:
+ * -------------------------------------------------------------------------------
+ * lookup3.c, by Bob Jenkins, May 2006, Public Domain.
+ *
+ * These are functions for producing 32-bit hashes for hash table lookup.
+ * hashword(), hashlittle(), hashlittle2(), hashbig(), mix(), and final()
+ * are externally useful functions.  Routines to test the hash are included
+ * if SELF_TEST is defined.  You can use this free for any purpose.  It's in
+ * the public domain.  It has no warranty.
+ *
+ * You probably want to use hashlittle().  hashlittle() and hashbig()
+ * hash byte arrays.  hashlittle() is is faster than hashbig() on
+ * little-endian machines.  Intel and AMD are little-endian machines.
+ * On second thought, you probably want hashlittle2(), which is identical to
+ * hashlittle() except it returns two 32-bit hashes for the price of one.
+ * You could implement hashbig2() if you wanted but I haven't bothered here.
+ *
+ * If you want to find a hash of, say, exactly 7 integers, do
+ *   a = i1;  b = i2;  c = i3;
+ *   mix(a, b, c);
+ *   a += i4; b += i5; c += i6;
+ *   mix(a, b, c);
+ *   a += i7;
+ *   finalMix(a, b, c);
+ * then use c as the hash value.  If you have a variable length array of
+ * 4-byte integers to hash, use hashword().  If you have a byte array (like
+ * a character string), use hashlittle().  If you have several byte arrays, or
+ * a mix of things, see the comments above hashlittle().
+ *
+ * Why is this so big?  I read 12 bytes at a time into 3 4-byte integers,
+ * then mix those integers.  This is fast (you can do a lot more thorough
+ * mixing with 12*3 instructions on 3 integers than you can with 3 instructions
+ * on 1 byte), but shoehorning those bytes into integers efficiently is messy.
+ *******************************************************************************/
+
+package org.eclipse.cdt.internal.core.parser.scanner;
+
+/**
+ * Computes a 64-bit hash value of a character stream that can be supplied one chunk at a time.
+ * Usage:
+ * <pre>
+ *   StreamHasher hasher = new StreamHasher();
+ *   for (long offset = 0; offset < streamLength; offset += chunkLength) {
+ *     hasher.addChunk(offset, chunkOfCharacters);
+ *   }
+ *   int64 hashValue = hasher.computeHash();
+ * </pre>
+ *
+ * Based on lookup3.c by Bob Jenkins from {@link "http://burtleburtle.net/bob/c/lookup3.c"}
+ */
+public final class StreamHasher {
+	private static final long SEED = 3141592653589793238L;  // PI
+	private static final long EMPTY_STRING_HASH = new StreamHasher().computeHashInternal();
+
+	long hashedOffset;  // Current position in the stream of characters.
+	int state;  // Current position in the stream of characters modulo 6, or -1 after computeHash is called.
+	int a;
+	int b;
+	int c;
+	char previousCharacter;
+
+	public StreamHasher() {
+		// Set up the internal state.
+		hashedOffset = 0;
+		state = 0;
+		a = b = c = (int) SEED;
+		c += SEED >>> 32;
+	}
+
+	/**
+	 * Adds a chunk of data to the hasher.
+	 * @param chunk Contents of the chunk.
+	 */
+	public void addChunk(char[] chunk) {
+		for (int pos = 0; pos < chunk.length; pos++, hashedOffset++) {
+			char cc = chunk[pos];
+			switch (state++) {
+			case -1:
+				throw new IllegalStateException("addChunk is called after computeHash."); //$NON-NLS-1$
+			case 0:
+			case 2:
+			case 4:
+				previousCharacter = cc;
+				break;
+			case 1:
+				a += previousCharacter | (cc << 16);
+				break;
+			case 3:
+				b += previousCharacter | (cc << 16);
+				break;
+			case 5:
+				c += previousCharacter | (cc << 16);
+				mix();
+				state = 0;
+				break;
+			}
+		}
+	}
+
+	/**
+	 * Computes and returns the hash value. Must be called once after the last chunk.
+	 * @return The hash value of the character stream.
+	 */
+	public long computeHash() {
+		if (state < 0) {
+			throw new IllegalStateException("computeHash method is called more than once."); //$NON-NLS-1$
+		}
+		return computeHashInternal() ^ EMPTY_STRING_HASH;
+	}
+
+	private long computeHashInternal() {
+		switch (state) {
+		case 1:
+			a += previousCharacter;
+			break;
+		case 3:
+			b += previousCharacter;
+			break;
+		case 5:
+			c += previousCharacter;
+			break;
+		}
+		state = -1;  // Protect against subsequent calls.
+		finalMix();
+		return (c & 0xFFFFFFFFL) | ((long) b << 32);
+	}
+
+	/**
+	 * Computes a 64-bit hash value of a String. The resulting hash value
+	 * is zero if the string is empty.
+	 *
+	 * @param str The string to hash.
+	 * @return The hash value.
+	 */
+	public static long hash(String str) {
+		StreamHasher hasher = new StreamHasher();
+		hasher.addChunk(str.toCharArray());
+		return hasher.computeHash();
+	}
+
+	/**
+	 * Mixes three 32-bit values reversibly.
+	 *
+	 * This is reversible, so any information in a, b, c before mix() is
+	 * still in a, b, c after mix().
+     *
+     * If four pairs of a, b, c inputs are run through mix(), or through
+	 * mix() in reverse, there are at least 32 bits of the output that
+	 * are sometimes the same for one pair and different for another pair.
+	 * This was tested for:
+	 * * pairs that differed by one bit, by two bits, in any combination
+	 *   of top bits of a, b, c, or in any combination of bottom bits of
+	 *   a, b, c.
+	 * * "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
+	 *   the output delta to a Gray code (a ^ (a >> 1)) so a string of 1's
+	 *   (as is commonly produced by subtraction) look like a single 1-bit
+	 *   difference.
+	 * * the base values were pseudo-random, all zero but one bit set, or
+	 *   all zero plus a counter that starts at zero.
+     *
+	 * Some k values for my "a -= c; a ^= Integer.rotateLeft(c, k); c += b;"
+	 * arrangement that satisfy this are
+	 *     4  6  8 16 19  4
+	 *     9 15  3 18 27 15
+	 *    14  9  3  7 17  3
+	 * Well, "9 15 3 18 27 15" didn't quite get 32 bits diffing
+	 * for "differ" defined as + with a one-bit base and a two-bit delta.
+	 * I used http://burtleburtle.net/bob/hash/avalanche.html to choose
+	 * the operations, constants, and arrangements of the variables.
+     *
+	 * This does not achieve avalanche.  There are input bits of a, b, c
+	 * that fail to affect some output bits of a, b, c, especially of a.
+	 * The most thoroughly mixed value is c, but it doesn't really even
+	 * achieve avalanche in c.
+     *
+	 * This allows some parallelism.  Read-after-writes are good at doubling
+	 * the number of bits affected, so the goal of mixing pulls in the opposite
+	 * direction as the goal of parallelism.  I did what I could.  Rotates
+	 * seem to cost as much as shifts on every machine I could lay my hands
+	 * on, and rotates are much kinder to the top and bottom bits, so I used
+	 * rotates.
+	 */
+	private void mix() {
+		a -= c;  a ^= Integer.rotateLeft(c, 4);  c += b;
+		b -= a;  b ^= Integer.rotateLeft(a, 6);  a += c;
+		c -= b;  c ^= Integer.rotateLeft(b, 8);  b += a;
+		a -= c;  a ^= Integer.rotateLeft(c, 16); c += b;
+		b -= a;  b ^= Integer.rotateLeft(a, 19); a += c;
+		c -= b;  c ^= Integer.rotateLeft(b, 4);  b += a;
+	}
+
+	/**
+	 * Final mixing of 3 32-bit values a, b, c into c
+     *
+	 * Pairs of a, b, c values differing in only a few bits will usually
+	 * produce values of c that look totally different.  This was tested for
+	 * * pairs that differed by one bit, by two bits, in any combination
+	 *   of top bits of a, b, c, or in any combination of bottom bits of
+	 *   a, b, c.
+	 * * "differ" is defined as +, -, ^, or ~^.  For + and -, I transformed
+	 *   the output delta to a Gray code (a ^ (a >> 1)) so a string of 1's (as
+	 *   is commonly produced by subtraction) look like a single 1-bit
+	 *   difference.
+	 * * the base values were pseudo-random, all zero but one bit set, or
+	 *   all zero plus a counter that starts at zero.
+	 *
+	 * These constants passed:
+	 *  14 11 25 16 4 14 24
+	 *  12 14 25 16 4 14 24
+	 * and these came close:
+	 *   4  8 15 26 3 22 24
+	 *  10  8 15 26 3 22 24
+	 *  11  8 15 26 3 22 24
+	 */
+	private void finalMix() {
+		c ^= b; c -= Integer.rotateLeft(b, 14);
+		a ^= c; a -= Integer.rotateLeft(c, 11);
+		b ^= a; b -= Integer.rotateLeft(a, 25);
+		c ^= b; c -= Integer.rotateLeft(b, 16);
+		a ^= c; a -= Integer.rotateLeft(c, 4);
+		b ^= a; b -= Integer.rotateLeft(a, 14);
+		c ^= b; c -= Integer.rotateLeft(b, 24);
+	}
+}

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/AbstractIndexerTask.java

@@ -50,6 +50,7 @@ import org.eclipse.cdt.internal.core.index.IIndexFragment;
 import org.eclipse.cdt.internal.core.index.IIndexFragmentFile;
 import org.eclipse.cdt.internal.core.index.IWritableIndex;
 import org.eclipse.cdt.internal.core.index.IndexBasedFileContentProvider;
+import org.eclipse.cdt.internal.core.parser.scanner.StreamHasher;
 import org.eclipse.cdt.internal.core.parser.scanner.InternalFileContentProvider;
 import org.eclipse.cdt.internal.core.pdom.dom.PDOMNotImplementedError;
 import org.eclipse.core.runtime.Assert;
@@ -245,9 +246,8 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 	}
 	
 
-	private final IASTTranslationUnit createAST(Object tu, AbstractLanguage language, IScannerInfo scanInfo, int options, 
+	private final IASTTranslationUnit createAST(Object tu, AbstractLanguage language, FileContent codeReader,
-			boolean inContext, IProgressMonitor pm) throws CoreException {
+			IScannerInfo scanInfo, int options, boolean inContext, IProgressMonitor pm) throws CoreException {
-		final FileContent codeReader= fResolver.getCodeReader(tu);
 		if (codeReader == null) {
 			return null;
 		}
@@ -368,6 +368,7 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 			IProgressMonitor monitor) throws CoreException {
 		final boolean forceAll= (fUpdateFlags & IIndexManager.UPDATE_ALL) != 0;
 		final boolean checkTimestamps= (fUpdateFlags & IIndexManager.UPDATE_CHECK_TIMESTAMPS) != 0;
+		final boolean checkFileContentsHash = (fUpdateFlags & IIndexManager.UPDATE_CHECK_CONTENTS_HASH) != 0;
 		final boolean checkConfig= (fUpdateFlags & IIndexManager.UPDATE_CHECK_CONFIGURATION) != 0;
 
 		int count= 0;
@@ -401,7 +402,7 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 						if (checkConfig) {
 							update= isSourceUnit ? isSourceUnitConfigChange(tu, ifile) : isHeaderConfigChange(tu, ifile);
 						}
-						update= update || force || (checkTimestamps && fResolver.getLastModified(ifl) != ifile.getTimestamp());
+						update= update || force || isModified(checkTimestamps, checkFileContentsHash, ifl, tu, ifile);
 						if (update) {
 							requestUpdate(linkageID, ifl, ifile);
 							store(tu, linkageID, isSourceUnit, files);
@@ -423,7 +424,7 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 						if (checkConfig) {
 							update= isHeaderConfigChange(tu, ifile);
 						}
-						update= update || force || (checkTimestamps && fResolver.getLastModified(ifl) != ifile.getTimestamp());
+						update= update || force || isModified(checkTimestamps, checkFileContentsHash, ifl, tu, ifile);
 						if (update) {
 							final int linkageID = ifile.getLinkageID();
 							requestUpdate(linkageID, ifl, ifile);
@@ -437,7 +438,18 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 		updateRequestedFiles(count - fFilesToUpdate.length);
 		fFilesToUpdate= null;
 	}
-	
+
+	private boolean isModified(boolean checkTimestamps, boolean checkFileContentsHash, IIndexFileLocation ifl,
+			Object tu, IIndexFragmentFile file)	throws CoreException {
+		boolean timestampDifferent = checkTimestamps && fResolver.getLastModified(ifl) != file.getTimestamp();
+		if (timestampDifferent) {
+			if (checkFileContentsHash && computeFileContentsHash(tu) == file.getContentsHash()) {
+				return false;
+			}
+		}
+		return timestampDifferent;
+	}
+
 	private void requestUpdate(int linkageID, IIndexFileLocation ifl, IIndexFragmentFile ifile) {
 		FileKey key= new FileKey(linkageID, ifl.getURI());
 		IndexFileContent info= fFileInfos.get(key);
@@ -589,7 +601,8 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 									}
 								}
 							}
-							writeToIndex(linkageID, ast, computeHashCode(scanInfo), monitor);
+							writeToIndex(linkageID, ast, StreamHasher.hash(code), computeHashCode(scanInfo),
+									monitor);
 							updateFileCount(0, 0, 1);
 						}
 					}
@@ -734,10 +747,11 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 			pm.subTask(getMessage(MessageKind.parsingFileTask,
 					path.lastSegment(), path.removeLastSegments(1).toString()));
 			long start= System.currentTimeMillis();
-			IASTTranslationUnit ast= createAST(tu, lang, scanInfo, fASTOptions, inContext, pm);
+			FileContent codeReader= fResolver.getCodeReader(tu);
+			IASTTranslationUnit ast= createAST(tu, lang, codeReader, scanInfo, fASTOptions, inContext, pm);
 			fStatistics.fParsingTime += System.currentTimeMillis() - start;
 			if (ast != null) {
-				writeToIndex(linkageID, ast, computeHashCode(scanInfo), pm);
+				writeToIndex(linkageID, ast, codeReader.getContentsHash(), computeHashCode(scanInfo), pm);
 			}
 		} catch (CoreException e) {
 			th= e;
@@ -755,8 +769,8 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 		}
 	}
 	
-	private void writeToIndex(final int linkageID, IASTTranslationUnit ast, int configHash,
+	private void writeToIndex(final int linkageID, IASTTranslationUnit ast, long fileContentsHash,
-			IProgressMonitor pm) throws CoreException, InterruptedException {
+			int configHash, IProgressMonitor pm) throws CoreException, InterruptedException {
 		HashSet<IIndexFileLocation> enteredFiles= new HashSet<IIndexFileLocation>();
 		ArrayList<IIndexFileLocation> orderedIFLs= new ArrayList<IIndexFileLocation>();
 		
@@ -775,7 +789,7 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 		
 		IIndexFileLocation[] ifls= orderedIFLs.toArray(new IIndexFileLocation[orderedIFLs.size()]);
 		try {
-			addSymbols(ast, ifls, fIndex, 1, false, configHash, fTodoTaskUpdater, pm);
+			addSymbols(ast, ifls, fIndex, 1, false, fileContentsHash, configHash, fTodoTaskUpdater, pm);
 		} finally {
 			// mark as updated in any case, to avoid parsing files that caused an exception to be thrown.
 			for (IIndexFileLocation ifl : ifls) {
@@ -940,6 +954,11 @@ public abstract class AbstractIndexerTask extends PDOMWriter {
 		return result * 31 + key.hashCode();
 	}
 
+	private long computeFileContentsHash(Object tu) {
+		FileContent codeReader= fResolver.getCodeReader(tu);
+		return codeReader != null ? codeReader.getContentsHash() : 0;
+	}
+
 	public final IndexFileContent getFileContent(int linkageID, IIndexFileLocation ifl) throws CoreException {
 		if (!needToUpdateHeader(linkageID, ifl)) {
 			IndexFileContent info= getFileInfo(linkageID, ifl);

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/IndexUpdatePolicy.java

@@ -140,7 +140,8 @@ public class IndexUpdatePolicy {
 		}
 		else if (fIndexer != null) {
 			if (oldPolicy == MANUAL) {
-				task= new PDOMUpdateTask(fIndexer, IIndexManager.UPDATE_CHECK_TIMESTAMPS);
+				task= new PDOMUpdateTask(fIndexer,
+						IIndexManager.UPDATE_CHECK_TIMESTAMPS | IIndexManager.UPDATE_CHECK_CONTENTS_HASH);
 				clearTUs();
 			}
 			else if (fKind == POST_CHANGE) {

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/PDOM.java

@@ -191,10 +191,11 @@ public class PDOM extends PlatformObject implements IPDOM {
 	 *  94.0 - new model for storing types, bug 294306.
 	 *  95.0 - parameter packs, bug 294730.
 	 *  96.0 - storing pack expansions in the template parameter map, bug 294730.
+	 *  97.0 - storing file contents hash in PDOMFile, bug 302083.
 	 */
-	private static final int MIN_SUPPORTED_VERSION= version(96, 0);
+	private static final int MIN_SUPPORTED_VERSION= version(97, 0);
-	private static final int MAX_SUPPORTED_VERSION= version(96, Short.MAX_VALUE);
+	private static final int MAX_SUPPORTED_VERSION= version(97, Short.MAX_VALUE);
-	private static final int DEFAULT_VERSION = version(96, 0);
+	private static final int DEFAULT_VERSION = version(97, 0);
 	
 	private static int version(int major, int minor) {
 		return (major << 16) + minor;

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/PDOMManager.java

@@ -571,7 +571,8 @@ public class PDOMManager implements IWritableIndexManager, IListener {
 							pdom.releaseReadLock();
 						}
 						if (resume) {
-							enqueue(new PDOMUpdateTask(indexer, IIndexManager.UPDATE_CHECK_TIMESTAMPS));
+							enqueue(new PDOMUpdateTask(indexer,
+									IIndexManager.UPDATE_CHECK_TIMESTAMPS | IIndexManager.UPDATE_CHECK_CONTENTS_HASH));
 						}
 					}
 					return;
@@ -592,7 +593,8 @@ public class PDOMManager implements IWritableIndexManager, IListener {
 
 				IPDOMIndexerTask task= null;
 				if (operation.wasSuccessful()) {
-					task= new PDOMUpdateTask(indexer, IIndexManager.UPDATE_CHECK_TIMESTAMPS);
+					task= new PDOMUpdateTask(indexer,
+							IIndexManager.UPDATE_CHECK_TIMESTAMPS | IIndexManager.UPDATE_CHECK_CONTENTS_HASH);
 				}
 				else {
 					task= new PDOMRebuildTask(indexer);

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/PDOMWriter.java

@@ -138,15 +138,15 @@ abstract public class PDOMWriter {
 	}
 			
 	/**
-	 * Extracts symbols from the given ast and adds them to the index. 
+	 * Extracts symbols from the given AST and adds them to the index. 
 	 * 
 	 * When flushIndex is set to <code>false</code>, you must make sure to flush the 
 	 * index after your last write operation.
 	 * @since 4.0
 	 */
 	public void addSymbols(IASTTranslationUnit ast, IIndexFileLocation[] ifls, IWritableIndex index, 
-			int readlockCount, boolean flushIndex, int configHash, ITodoTaskUpdater taskUpdater,
+			int readlockCount, boolean flushIndex, long fileContentsHash, int configHash,
-			IProgressMonitor pm) throws InterruptedException, CoreException {
+			ITodoTaskUpdater taskUpdater, IProgressMonitor pm) throws InterruptedException, CoreException {
 		if (fShowProblems) {
 			fShowInclusionProblems= true;
 			fShowScannerProblems= true;
@@ -165,8 +165,8 @@ abstract public class PDOMWriter {
 		resolveNames(symbolMap, ifls, stati, pm);
 
 		// index update
-		storeSymbolsInIndex(symbolMap, ifls, ast.getLinkage().getLinkageID(), configHash, contextIncludes,
+		storeSymbolsInIndex(symbolMap, ifls, ast.getLinkage().getLinkageID(), fileContentsHash,
-				index, readlockCount, flushIndex, stati, pm);
+				configHash, contextIncludes, index, readlockCount, flushIndex, stati, pm);
 
 		if (taskUpdater != null) {
 			taskUpdater.updateTasks(ast.getComments(), ifls);
@@ -193,9 +193,10 @@ abstract public class PDOMWriter {
 	}
 
 	private void storeSymbolsInIndex(final Map<IIndexFileLocation, Symbols> symbolMap, IIndexFileLocation[] ifls,
-			int linkageID, int configHash, HashSet<IASTPreprocessorIncludeStatement> contextIncludes,
+			int linkageID, long fileContentsHash, int configHash,
-			IWritableIndex index, int readlockCount, boolean flushIndex,
+			HashSet<IASTPreprocessorIncludeStatement> contextIncludes, IWritableIndex index, int readlockCount,
-			ArrayList<IStatus> stati, IProgressMonitor pm) throws InterruptedException, CoreException {
+			boolean flushIndex, ArrayList<IStatus> stati, IProgressMonitor pm)
+			throws InterruptedException, CoreException {
 		for (int i= 0; i < ifls.length; i++) {
 			if (pm.isCanceled()) 
 				return;
@@ -209,7 +210,8 @@ abstract public class PDOMWriter {
 				YieldableIndexLock lock = new YieldableIndexLock(index, readlockCount, flushIndex);
 				lock.acquire();
 				try {
-					storeFileInIndex(index, ifl, symbolMap, linkageID, configHash, contextIncludes, lock);
+					storeFileInIndex(index, ifl, symbolMap, linkageID, fileContentsHash, configHash,
+							contextIncludes, lock);
 				} catch (RuntimeException e) {
 					th= e; 
 				} catch (PDOMNotImplementedError e) {
@@ -457,9 +459,9 @@ abstract public class PDOMWriter {
 	}
 
 	private IIndexFragmentFile storeFileInIndex(IWritableIndex index, IIndexFileLocation location,
-			Map<IIndexFileLocation, Symbols> symbolMap, int linkageID, int configHash,
+			Map<IIndexFileLocation, Symbols> symbolMap, int linkageID, long fileContentsHash,
-			Set<IASTPreprocessorIncludeStatement> contextIncludes, YieldableIndexLock lock)
+			int configHash, Set<IASTPreprocessorIncludeStatement> contextIncludes,
-			throws CoreException, InterruptedException {
+			YieldableIndexLock lock) throws CoreException, InterruptedException {
 		Set<IIndexFileLocation> clearedContexts= Collections.emptySet();
 		IIndexFragmentFile file;
 		long timestamp = fResolver.getLastModified(location);
@@ -518,6 +520,7 @@ abstract public class PDOMWriter {
 			}
 			if (SEMI_TRANSACTIONAL_UPDATES) {
 				file.setTimestamp(timestamp);
+				file.setContentsHash(fileContentsHash);
 				file = index.commitUncommittedFile();
 			}
 		} finally {

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/dom/PDOMFile.java

@@ -71,11 +71,12 @@ public class PDOMFile implements IIndexFragmentFile {
 	private static final int LOCATION_REPRESENTATION = 16;
 	private static final int LINKAGE_ID= 20;
 	private static final int TIME_STAMP = 24;
-	private static final int SCANNER_CONFIG_HASH= 32;
+	private static final int CONTENT_HASH= 32;
-	private static final int LAST_USING_DIRECTIVE= 36;
+	private static final int SCANNER_CONFIG_HASH= 40;
-	private static final int FIRST_MACRO_REFERENCE= 40;
+	private static final int LAST_USING_DIRECTIVE= 44;
+	private static final int FIRST_MACRO_REFERENCE= 48;
 
-	private static final int RECORD_SIZE= 44;
+	private static final int RECORD_SIZE= 52;
 
 	public static class Comparator implements IBTreeComparator {
 		private Database db;
@@ -223,6 +224,7 @@ public class PDOMFile implements IIndexFragmentFile {
 		}
 
 		setTimestamp(sourceFile.getTimestamp());
+		setContentsHash(sourceFile.getContentsHash());
 		setScannerConfigurationHashcode(sourceFile.getScannerConfigurationHashcode());
 
 		sourceFile.delete();
@@ -271,6 +273,16 @@ public class PDOMFile implements IIndexFragmentFile {
 		db.putLong(record + TIME_STAMP, timestamp);
 	}
 
+	public long getContentsHash() throws CoreException {
+		Database db = fLinkage.getDB();
+		return db.getLong(record + CONTENT_HASH);
+	}
+
+	public void setContentsHash(long hash) throws CoreException {
+		Database db= fLinkage.getDB();
+		db.putLong(record + CONTENT_HASH, hash);
+	}
+
 	public int getScannerConfigurationHashcode() throws CoreException {
 		Database db = fLinkage.getDB();
 		return db.getInt(record + SCANNER_CONFIG_HASH);

core/org.eclipse.cdt.core/parser/org/eclipse/cdt/internal/core/pdom/indexer/PDOMIndexerTask.java

@@ -99,7 +99,7 @@ public abstract class PDOMIndexerTask extends AbstractIndexerTask implements IPD
 			setIndexFilesWithoutBuildConfiguration(false);
 			setIndexHeadersWithoutContext(UnusedHeaderStrategy.skip);
 		}
-		setUpdateFlags(IIndexManager.UPDATE_CHECK_TIMESTAMPS);
+		setUpdateFlags(IIndexManager.UPDATE_CHECK_TIMESTAMPS | IIndexManager.UPDATE_CHECK_CONTENTS_HASH);
 		setForceFirstFiles(forceFiles.length);
 	}
 	

core/org.eclipse.cdt.ui/src/org/eclipse/cdt/internal/ui/actions/UpdateIndexWithModifiedFilesAction.java

@@ -16,6 +16,7 @@ public class UpdateIndexWithModifiedFilesAction extends AbstractUpdateIndexActio
 
 	@Override
 	protected int getUpdateOptions() {
-		return IIndexManager.UPDATE_CHECK_TIMESTAMPS | IIndexManager.UPDATE_CHECK_CONFIGURATION | IIndexManager.UPDATE_EXTERNAL_FILES_FOR_PROJECT;
+		return IIndexManager.UPDATE_CHECK_TIMESTAMPS | IIndexManager.UPDATE_CHECK_CONFIGURATION |
+		IIndexManager.UPDATE_EXTERNAL_FILES_FOR_PROJECT | IIndexManager.UPDATE_CHECK_CONTENTS_HASH;
 	}
 }