From e488f1cacd7813feaca9f7d7b09de7eb5ec69f84 Mon Sep 17 00:00:00 2001
From: "Shawn O. Pearce" <spearce@spearce.org>
Date: Wed, 3 Nov 2010 19:01:53 -0700
Subject: [PATCH] Add MutableObjectId setByte to modify a mutable id

This mirrors the getByte() API in ObjectId and allows the caller to
modify a single byte, which is useful when updating it as part of a
loop walking through 0x00..0xff inside of a range of objects.

Change-Id: I57fa8420011fe5ed5fc6bfeb26f87a02b3197dab
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
---
 .../org/eclipse/jgit/lib/ObjectIdTest.java    | 29 ++++++++++
 .../org/eclipse/jgit/lib/MutableObjectId.java | 54 +++++++++++++++++++
 2 files changed, 83 insertions(+)

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ObjectIdTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ObjectIdTest.java
index 2eb1e6b9e1..e5faff15ed 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ObjectIdTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ObjectIdTest.java
@@ -122,4 +122,33 @@ public class ObjectIdTest extends TestCase {
 		for (int i = 2; i < 20; i++)
 			assertEquals("index " + i, raw[i] & 0xff, id.getByte(i));
 	}
+
+	public void testSetByte() {
+		byte[] exp = new byte[20];
+		for (int i = 0; i < 20; i++)
+			exp[i] = (byte) (0xa0 + i);
+
+		MutableObjectId id = new MutableObjectId();
+		id.fromRaw(exp);
+		assertEquals(ObjectId.fromRaw(exp).name(), id.name());
+
+		id.setByte(0, 0x10);
+		assertEquals(0x10, id.getByte(0));
+		exp[0] = 0x10;
+		assertEquals(ObjectId.fromRaw(exp).name(), id.name());
+
+		for (int p = 1; p < 20; p++) {
+			id.setByte(p, 0x10 + p);
+			assertEquals(0x10 + p, id.getByte(p));
+			exp[p] = (byte) (0x10 + p);
+			assertEquals(ObjectId.fromRaw(exp).name(), id.name());
+		}
+
+		for (int p = 0; p < 20; p++) {
+			id.setByte(p, 0x80 + p);
+			assertEquals(0x80 + p, id.getByte(p));
+			exp[p] = (byte) (0x80 + p);
+			assertEquals(ObjectId.fromRaw(exp).name(), id.name());
+		}
+	}
 }
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/MutableObjectId.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/MutableObjectId.java
index 26e83d423b..7d7dfc2f1a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/MutableObjectId.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/MutableObjectId.java
@@ -74,6 +74,60 @@ public class MutableObjectId extends AnyObjectId {
 		fromObjectId(src);
 	}
 
+	/**
+	 * Set any byte in the id.
+	 *
+	 * @param index
+	 *            index of the byte to set in the raw form of the ObjectId. Must
+	 *            be in range [0, {@link Constants#OBJECT_ID_LENGTH}).
+	 * @param value
+	 *            the value of the specified byte at {@code index}. Values are
+	 *            unsigned and thus are in the range [0,255] rather than the
+	 *            signed byte range of [-128, 127].
+	 * @throws ArrayIndexOutOfBoundsException
+	 *             {@code index} is less than 0, equal to
+	 *             {@link Constants#OBJECT_ID_LENGTH}, or greater than
+	 *             {@link Constants#OBJECT_ID_LENGTH}.
+	 */
+	public void setByte(int index, int value) {
+		switch (index >> 2) {
+		case 0:
+			w1 = set(w1, index & 3, value);
+			break;
+		case 1:
+			w2 = set(w2, index & 3, value);
+			break;
+		case 2:
+			w3 = set(w3, index & 3, value);
+			break;
+		case 3:
+			w4 = set(w4, index & 3, value);
+			break;
+		case 4:
+			w5 = set(w5, index & 3, value);
+			break;
+		default:
+			throw new ArrayIndexOutOfBoundsException(index);
+		}
+	}
+
+	private static int set(int w, int index, int value) {
+		value &= 0xff;
+
+		switch (index) {
+		case 0:
+			return (w & 0x00ffffff) | (value << 24);
+		case 1:
+			return (w & 0xff00ffff) | (value << 16);
+		case 2:
+			return (w & 0xffff00ff) | (value << 8);
+		case 3:
+			return (w & 0xffffff00) | value;
+		default:
+			throw new ArrayIndexOutOfBoundsException();
+		}
+	}
+
 	/** Make this id match {@link ObjectId#zeroId()}. */
 	public void clear() {
 		w1 = 0;
-- 
2.39.5