Replace usage of ArrayIndexOutOfBoundsException in treewalk

Using exceptions during normal operations - for example with the
desire of expanding an array in the failure case - can have a
severe performance impact. When exceptions are instantiated,
a stack trace is collected. Generating stack trace can be expensive.

Compared to that, checking an array for length - even if done many
times - is cheap since this is a check that can run in just a
handful of CPU cycles.

Change-Id: Ifaf10623f6a876c9faecfa44654c9296315adfcb
Signed-off-by: Patrick Hiesel <hiesel@google.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/AbstractTreeIterator.java

@@ -239,12 +239,10 @@ public abstract class AbstractTreeIterator {
 		path = p.path;
 		pathOffset = p.pathLen + 1;
 
-		try {
-			path[pathOffset - 1] = '/';
-		} catch (ArrayIndexOutOfBoundsException e) {
+		if (pathOffset > path.length) {
 			growPath(p.pathLen);
-			path[pathOffset - 1] = '/';
 		}
+		path[pathOffset - 1] = '/';
 	}
 
 	/**

org.eclipse.jgit/src/org/eclipse/jgit/treewalk/CanonicalTreeParser.java

@@ -387,14 +387,13 @@ public class CanonicalTreeParser extends AbstractTreeIterator {
 		tmp = pathOffset;
 		for (;; tmp++) {
 			c = raw[ptr++];
-			if (c == 0)
+			if (c == 0) {
 				break;
-			try {
-				path[tmp] = c;
-			} catch (ArrayIndexOutOfBoundsException e) {
+			}
+			if (tmp >= path.length) {
 				growPath(tmp);
-				path[tmp] = c;
 			}
+			path[tmp] = c;
 		}
 		pathLen = tmp;
 		nextPtr = ptr + OBJECT_ID_LENGTH;