From 6bf4bba9f875d1815989a94c39a27f01961d82bb Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers3@gmail.com>
Date: Sat, 22 Aug 2015 09:08:06 -0500
Subject: [PATCH] lzms_common.c: tweak opcode branching in lzms_x86_filter()

---
 src/lzms_common.c | 58 +++++++++++++++++++++++------------------------
 1 file changed, 29 insertions(+), 29 deletions(-)

diff --git a/src/lzms_common.c b/src/lzms_common.c
index 333beb5f..47c07117 100644
--- a/src/lzms_common.c
+++ b/src/lzms_common.c
@@ -446,26 +446,26 @@ translate_if_needed(u8 *data, u8 *p, s32 *last_x86_pos,
 
 	/*
 	 * p[0] has one of the following values:
-	 *	0xE8 0xE9 0x48 0x4C 0xF0 0xFF
+	 *	0x48 0x4C 0xE8 0xE9 0xF0 0xFF
 	 */
 
-	if ((p[0] & 0xFE) == 0xE8) {
-		if (p[0] & 0x01) {
-			/* 0xE9: Jump relative.  Theoretically this would be
-			 * useful to translate, but in fact it's explicitly
-			 * excluded.  Most likely it creates too many false
-			 * positives for the detection algorithm.  */
-			p += 4;
+	if (p[0] >= 0xF0) {
+		if (p[0] & 0x0F) {
+			/* 0xFF (instruction group)  */
+			if (p[1] == 0x15) {
+				/* Call indirect relative  */
+				opcode_nbytes = 2;
+				goto have_opcode;
+			}
 		} else {
-			/* 0xE8: Call relative.  This is a common case, so it
-			 * uses a reduced max_trans_offset.  In other words, we
-			 * have to be more confident that the data actually is
-			 * x86 machine code before we'll do the translation.  */
-			opcode_nbytes = 1;
-			max_trans_offset >>= 1;
-			goto have_opcode;
+			/* 0xF0 (lock prefix)  */
+			if (p[1] == 0x83 && p[2] == 0x05) {
+				/* Lock add relative  */
+				opcode_nbytes = 3;
+				goto have_opcode;
+			}
 		}
-	} else if ((p[0] & 0xFB) == 0x48) {
+	} else if (p[0] <= 0x4C) {
 
 		/* 0x48 or 0x4C.  In 64-bit code this is a REX prefix byte with
 		 * W=1, R=[01], X=0, and B=0, and it will be followed by the
@@ -492,20 +492,20 @@ translate_if_needed(u8 *data, u8 *p, s32 *last_x86_pos,
 			}
 		}
 	} else {
-		if (p[0] & 0x0F) {
-			/* 0xFF (instruction group)  */
-			if (p[1] == 0x15) {
-				/* Call indirect relative  */
-				opcode_nbytes = 2;
-				goto have_opcode;
-			}
+		if (p[0] & 0x01) {
+			/* 0xE9: Jump relative.  Theoretically this would be
+			 * useful to translate, but in fact it's explicitly
+			 * excluded.  Most likely it creates too many false
+			 * positives for the detection algorithm.  */
+			p += 4;
 		} else {
-			/* 0xF0 (lock prefix)  */
-			if (p[1] == 0x83 && p[2] == 0x05) {
-				/* Lock add relative  */
-				opcode_nbytes = 3;
-				goto have_opcode;
-			}
+			/* 0xE8: Call relative.  This is a common case, so it
+			 * uses a reduced max_trans_offset.  In other words, we
+			 * have to be more confident that the data actually is
+			 * x86 machine code before we'll do the translation.  */
+			opcode_nbytes = 1;
+			max_trans_offset >>= 1;
+			goto have_opcode;
 		}
 	}
 
-- 
2.43.0