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 /*

  * Copyright (c) 2003, 2012, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  *

  */

 #ifndef SHARE_VM_RUNTIME_JFIELDIDWORKAROUND_HPP

 #define SHARE_VM_RUNTIME_JFIELDIDWORKAROUND_HPP

 class jfieldIDWorkaround: AllStatic {

   // This workaround is because JVMTI doesn't have distinct entry points

   // for methods that use static jfieldIDs and instance jfieldIDs.

   // The workaround is to steal a low-order bit:

   //   a 1 means the jfieldID is an instance jfieldID,

   //             and the rest of the word is the offset of the field.

   //   a 0 means the jfieldID is a static jfieldID,

   //             and the rest of the word is the JNIid*.

   //

   // Another low-order bit is used to mark if an instance field

   // is accompanied by an indication of which class it applies to.

   //

   // Bit-format of a jfieldID (most significant first):

   //  address:30        instance=0:1 checked=0:1

   //  offset:30         instance=1:1 checked=0:1

   //  klass:23 offset:7 instance=1:1 checked=1:1

   //

   // If the offset does not fit in 7 bits, or if the fieldID is

   // not checked, then the checked bit is zero and the rest of

   // the word (30 bits) contains only the offset.

   //

  private:

   enum {

     checked_bits           = 1,

     instance_bits          = 1,

     address_bits           = BitsPerWord - checked_bits - instance_bits,

     large_offset_bits      = address_bits,  // unioned with address

     small_offset_bits      = 7,

     klass_bits             = address_bits - small_offset_bits,

     checked_shift          = 0,

     instance_shift         = checked_shift  + checked_bits,

     address_shift          = instance_shift + instance_bits,

     offset_shift           = address_shift,  // unioned with address

     klass_shift            = offset_shift + small_offset_bits,

     checked_mask_in_place  = right_n_bits(checked_bits)  << checked_shift,

     instance_mask_in_place = right_n_bits(instance_bits) << instance_shift,

 #ifndef _WIN64

     large_offset_mask      = right_n_bits(large_offset_bits),

     small_offset_mask      = right_n_bits(small_offset_bits),

     klass_mask             = right_n_bits(klass_bits)

 #endif

     };

 #ifdef _WIN64

     // These values are too big for Win64

     const static uintptr_t large_offset_mask = right_n_bits(large_offset_bits);

     const static uintptr_t small_offset_mask = right_n_bits(small_offset_bits);

     const static uintptr_t klass_mask        = right_n_bits(klass_bits);

 #endif

   // helper routines:

   static bool is_checked_jfieldID(jfieldID id) {

     uintptr_t as_uint = (uintptr_t) id;

     return ((as_uint & checked_mask_in_place) != 0);

   }

   static intptr_t raw_instance_offset(jfieldID id) {

     uintptr_t result = (uintptr_t) id >> address_shift;

     if (VerifyJNIFields && is_checked_jfieldID(id)) {

       result &= small_offset_mask;  // cut off the hash bits

     }

     return (intptr_t)result;

   }

   static intptr_t encode_klass_hash(Klass* k, intptr_t offset);

   static bool             klass_hash_ok(Klass* k, jfieldID id);

   static void  verify_instance_jfieldID(Klass* k, jfieldID id);

  public:

   static bool is_valid_jfieldID(Klass* k, jfieldID id);

   static bool is_instance_jfieldID(Klass* k, jfieldID id) {

     uintptr_t as_uint = (uintptr_t) id;

     return ((as_uint & instance_mask_in_place) != 0);

   }

   static bool is_static_jfieldID(jfieldID id) {

     uintptr_t as_uint = (uintptr_t) id;

     return ((as_uint & instance_mask_in_place) == 0);

   }

   static jfieldID to_instance_jfieldID(Klass* k, int offset) {

     intptr_t as_uint = ((offset & large_offset_mask) << offset_shift) | instance_mask_in_place;

     if (VerifyJNIFields) {

       as_uint |= encode_klass_hash(k, offset);

     }

     jfieldID result = (jfieldID) as_uint;

 #ifndef ASSERT

     // always verify in debug mode; switchable in anything else

     if (VerifyJNIFields)

 #endif // ASSERT

     {

       verify_instance_jfieldID(k, result);

     }

     assert(raw_instance_offset(result) == (offset & large_offset_mask), "extract right offset");

     return result;

   }

   static intptr_t from_instance_jfieldID(Klass* k, jfieldID id) {

 #ifndef ASSERT

     // always verify in debug mode; switchable in anything else

     if (VerifyJNIFields)

 #endif // ASSERT

     {

       verify_instance_jfieldID(k, id);

     }

     return raw_instance_offset(id);

   }

   static jfieldID to_static_jfieldID(JNIid* id) {

     assert(id->is_static_field_id(), "from_JNIid, but not static field id");

     jfieldID result = (jfieldID) id;

     assert(from_static_jfieldID(result) == id, "must produce the same static id");

     return result;

   }

   static JNIid* from_static_jfieldID(jfieldID id) {

     assert(jfieldIDWorkaround::is_static_jfieldID(id),

            "to_JNIid, but not static jfieldID");

     JNIid* result = (JNIid*) id;

     assert(result->is_static_field_id(), "to_JNIid, but not static field id");

     return result;

   }

   static jfieldID to_jfieldID(instanceKlassHandle k, int offset, bool is_static) {

     if (is_static) {

       JNIid *id = k->jni_id_for(offset);

       debug_only(id->set_is_static_field_id());

       return jfieldIDWorkaround::to_static_jfieldID(id);

     } else {

       return jfieldIDWorkaround::to_instance_jfieldID(k(), offset);

     }

   }

 };

 #endif // SHARE_VM_RUNTIME_JFIELDIDWORKAROUND_HPP