From 2cde631fcaf486caf88ba5af436483abc6fc557d Mon Sep 17 00:00:00 2001
From: Graham <gpe@openrs2.dev>
Date: Fri, 2 Aug 2019 17:17:47 +0100
Subject: [PATCH] Add BitShiftTransformer

---
 .../java/dev/openrs2/asm/InsnNodeUtils.java   | 61 +++++++++++++++++++
 .../java/dev/openrs2/deob/Deobfuscator.java   |  2 +
 .../deob/transform/BitShiftTransformer.java   | 48 +++++++++++++++
 3 files changed, 111 insertions(+)
 create mode 100644 deob/src/main/java/dev/openrs2/deob/transform/BitShiftTransformer.java

diff --git a/asm/src/main/java/dev/openrs2/asm/InsnNodeUtils.java b/asm/src/main/java/dev/openrs2/asm/InsnNodeUtils.java
index a4ec526881..d5f0db55f7 100644
--- a/asm/src/main/java/dev/openrs2/asm/InsnNodeUtils.java
+++ b/asm/src/main/java/dev/openrs2/asm/InsnNodeUtils.java
@@ -1,6 +1,10 @@
 package dev.openrs2.asm;
 
+import org.objectweb.asm.Opcodes;
 import org.objectweb.asm.tree.AbstractInsnNode;
+import org.objectweb.asm.tree.InsnNode;
+import org.objectweb.asm.tree.IntInsnNode;
+import org.objectweb.asm.tree.LdcInsnNode;
 
 public final class InsnNodeUtils {
 	public static AbstractInsnNode nextReal(AbstractInsnNode insn) {
@@ -31,6 +35,63 @@ public final class InsnNodeUtils {
 		return insn;
 	}
 
+	public static int getIntConstant(AbstractInsnNode insn) {
+		switch (insn.getOpcode()) {
+		case Opcodes.ICONST_M1:
+			return -1;
+		case Opcodes.ICONST_0:
+			return 0;
+		case Opcodes.ICONST_1:
+			return 1;
+		case Opcodes.ICONST_2:
+			return 2;
+		case Opcodes.ICONST_3:
+			return 3;
+		case Opcodes.ICONST_4:
+			return 4;
+		case Opcodes.ICONST_5:
+			return 5;
+		case Opcodes.BIPUSH:
+		case Opcodes.SIPUSH:
+			var intInsn = (IntInsnNode) insn;
+			return intInsn.operand;
+		case Opcodes.LDC:
+			var ldc = (LdcInsnNode) insn;
+			if (ldc.cst instanceof Integer) {
+				return (Integer) ldc.cst;
+			}
+		}
+
+		throw new IllegalArgumentException();
+	}
+
+	public static AbstractInsnNode createIntConstant(int value) {
+		switch (value) {
+		case -1:
+			return new InsnNode(Opcodes.ICONST_M1);
+		case 0:
+			return new InsnNode(Opcodes.ICONST_0);
+		case 1:
+			return new InsnNode(Opcodes.ICONST_1);
+		case 2:
+			return new InsnNode(Opcodes.ICONST_2);
+		case 3:
+			return new InsnNode(Opcodes.ICONST_3);
+		case 4:
+			return new InsnNode(Opcodes.ICONST_4);
+		case 5:
+			return new InsnNode(Opcodes.ICONST_5);
+		}
+
+		if (value >= Byte.MIN_VALUE && value <= Byte.MAX_VALUE) {
+			return new IntInsnNode(Opcodes.BIPUSH, value);
+		} else if (value >= Short.MIN_VALUE && value <= Short.MAX_VALUE) {
+			return new IntInsnNode(Opcodes.SIPUSH, value);
+		} else {
+			return new LdcInsnNode(value);
+		}
+	}
+
 	private InsnNodeUtils() {
 		/* empty */
 	}
diff --git a/deob/src/main/java/dev/openrs2/deob/Deobfuscator.java b/deob/src/main/java/dev/openrs2/deob/Deobfuscator.java
index 492fcd0834..0329e3ecaa 100644
--- a/deob/src/main/java/dev/openrs2/deob/Deobfuscator.java
+++ b/deob/src/main/java/dev/openrs2/deob/Deobfuscator.java
@@ -11,6 +11,7 @@ import dev.openrs2.asm.Library;
 import dev.openrs2.asm.Transformer;
 import dev.openrs2.deob.classpath.ClassPath;
 import dev.openrs2.deob.classpath.TypedRemapper;
+import dev.openrs2.deob.transform.BitShiftTransformer;
 import dev.openrs2.deob.transform.CanvasTransformer;
 import dev.openrs2.deob.transform.ClassForNameTransformer;
 import dev.openrs2.deob.transform.CounterTransformer;
@@ -27,6 +28,7 @@ public final class Deobfuscator {
 	private static final List<Transformer> TRANSFORMERS = List.of(
 		new OpaquePredicateTransformer(),
 		new ExceptionTracingTransformer(),
+		new BitShiftTransformer(),
 		new CounterTransformer(),
 		new CanvasTransformer(),
 		new FieldOrderTransformer()
diff --git a/deob/src/main/java/dev/openrs2/deob/transform/BitShiftTransformer.java b/deob/src/main/java/dev/openrs2/deob/transform/BitShiftTransformer.java
new file mode 100644
index 0000000000..60146f0bbb
--- /dev/null
+++ b/deob/src/main/java/dev/openrs2/deob/transform/BitShiftTransformer.java
@@ -0,0 +1,48 @@
+package dev.openrs2.deob.transform;
+
+import java.util.Set;
+
+import dev.openrs2.asm.InsnMatcher;
+import dev.openrs2.asm.InsnNodeUtils;
+import dev.openrs2.asm.Library;
+import dev.openrs2.asm.Transformer;
+import org.objectweb.asm.Opcodes;
+import org.objectweb.asm.tree.ClassNode;
+import org.objectweb.asm.tree.MethodNode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public final class BitShiftTransformer extends Transformer {
+	private static final Logger logger = LoggerFactory.getLogger(BitShiftTransformer.class);
+
+	private static final InsnMatcher CONST_SHIFT_MATCHER = InsnMatcher.compile("(ICONST | BIPUSH | SIPUSH | LDC) (ISHL | ISHR | IUSHR | LSHL | LSHR | LUSHR)");
+	private static final Set<Integer> LONG_SHIFTS = Set.of(Opcodes.LSHL, Opcodes.LSHR, Opcodes.LUSHR);
+
+	private int simplified;
+
+	@Override
+	public void preTransform(Library library) {
+		simplified = 0;
+	}
+
+	@Override
+	public void transformCode(ClassNode clazz, MethodNode method) {
+		CONST_SHIFT_MATCHER.match(method).forEach(match -> {
+			var push = match.get(0);
+			var bits = InsnNodeUtils.getIntConstant(push);
+
+			var opcode = match.get(1).getOpcode();
+			var simplifiedBits = bits & (LONG_SHIFTS.contains(opcode) ? 63 : 31);
+
+			if (bits != simplifiedBits) {
+				method.instructions.set(push, InsnNodeUtils.createIntConstant(simplifiedBits));
+				simplified++;
+			}
+		});
+	}
+
+	@Override
+	public void postTransform(Library library) {
+		logger.info("Simplified {} bit shifts", simplified);
+	}
+}