Fix testing of the VEX.L (128/256-bit) flag in the x64 disassembler

src/x64/disasm-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <assert.h>
 #include <stdarg.h>
 #include <stdio.h>
 
 #if V8_TARGET_ARCH_X64
 
@@ skipping 341 matching lines @@
   bool rex_w() { return (rex_ & 0x08) != 0; }
 
   bool vex_w() {
     DCHECK(vex_byte0_ == VEX3_PREFIX || vex_byte0_ == VEX2_PREFIX);
     return vex_byte0_ == VEX3_PREFIX ? (vex_byte2_ & 0x80) != 0 : false;
   }
 
   bool vex_128() {
     DCHECK(vex_byte0_ == VEX3_PREFIX || vex_byte0_ == VEX2_PREFIX);
     byte checked = vex_byte0_ == VEX3_PREFIX ? vex_byte2_ : vex_byte1_;
-    return (checked & 4) != 1;
+    return (checked & 4) == 0;
   }
 
   bool vex_none() {
     DCHECK(vex_byte0_ == VEX3_PREFIX || vex_byte0_ == VEX2_PREFIX);
     byte checked = vex_byte0_ == VEX3_PREFIX ? vex_byte2_ : vex_byte1_;
     return (checked & 3) == 0;
   }
 
   bool vex_66() {
     DCHECK(vex_byte0_ == VEX3_PREFIX || vex_byte0_ == VEX2_PREFIX);
@@ skipping 2129 matching lines @@
     for (int i = 6 - static_cast<int>(pc - prev_pc); i >= 0; i--) {
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 }  // namespace disasm
 
 #endif  // V8_TARGET_ARCH_X64