Add InstructionOffsetMap utility class

This provides a convenient way to map back and forth between
instruction offsets and indexes within a method

dexlib2/src/main/java/org/jf/dexlib2/util/InstructionOffsetMap.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright 2012, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.jf.dexlib2.util;
+
+import org.jf.dexlib2.iface.MethodImplementation;
+import org.jf.dexlib2.iface.instruction.Instruction;
+import org.jf.util.ExceptionWithContext;
+
+import javax.annotation.Nonnull;
+import java.util.Arrays;
+import java.util.List;
+
+public class InstructionOffsetMap {
+    @Nonnull private final int[] instructionCodeOffsets;
+
+    public InstructionOffsetMap(@Nonnull MethodImplementation methodImpl) {
+        List<? extends Instruction> instructions = methodImpl.getInstructions();
+        int[] instructionCodeOffsets = new int[instructions.size()];
+
+        int codeOffset = 0;
+        for (int i=0; i<instructions.size(); i++) {
+            instructionCodeOffsets[i] = codeOffset;
+            //TODO: handle variable size instructions
+            codeOffset += instructions.get(i).getOpcode().format.size / 2;
+        }
+
+        this.instructionCodeOffsets = instructionCodeOffsets;
+    }
+
+    public int getInstructionIndexAtCodeOffset(int codeOffset, boolean exact) {
+        int index = Arrays.binarySearch(instructionCodeOffsets, codeOffset);
+        if (index < 0) {
+            if (exact) {
+                throw new ExceptionWithContext("No instruction at offset %d", codeOffset);
+            } else {
+                // This calculation would be incorrect if index was -1 (i.e. insertion point of 0). Luckily, we can
+                // ignore this case, because codeOffset will always be non-negative, and the code offset of the first
+                // instruction will always be 0.
+                return (~index) - 1;
+            }
+        }
+        return index;
+    }
+
+    public int getInstructionCodeOffset(int index) {
+        if (index < 0 || index >= instructionCodeOffsets.length) {
+            throw new ExceptionWithContext("Index out of bounds: %d", index);
+        }
+        return instructionCodeOffsets[index];
+    }
+}