/*

 * Copyright (c) 2003, 2017, 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(InstanceKlass* 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