/*

 * Copyright (c) 2008, 2013, 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.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * 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

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 */

package sun.invoke.util;

import java.lang.invoke.MethodType;

import sun.invoke.empty.Empty;

/**

 * This class centralizes information about the JVM verifier

 * and its requirements about type correctness.

 * @author jrose

 */

public class VerifyType {

    private VerifyType() { }  // cannot instantiate

    /**

     * True if a value can be stacked as the source type and unstacked as the

     * destination type, without violating the JVM's type consistency.

     *

     * @param src the type of a stacked value

     * @param dst the type by which we'd like to treat it

     * @return whether the retyping can be done without motion or reformatting

     */

    public static boolean isNullConversion(Class<?> src, Class<?> dst) {

        if (src == dst)            return true;

        // Verifier allows any interface to be treated as Object:

        if (dst.isInterface())     dst = Object.class;

        if (src.isInterface())     src = Object.class;

        if (src == dst)            return true;  // check again

        if (dst == void.class)     return true;  // drop any return value

        if (isNullType(src))       return !dst.isPrimitive();

        if (!src.isPrimitive())    return dst.isAssignableFrom(src);

        if (!dst.isPrimitive())    return false;

        // Verifier allows an int to carry byte, short, char, or even boolean:

        Wrapper sw = Wrapper.forPrimitiveType(src);

        if (dst == int.class)      return sw.isSubwordOrInt();

        Wrapper dw = Wrapper.forPrimitiveType(dst);

        if (!sw.isSubwordOrInt())  return false;

        if (!dw.isSubwordOrInt())  return false;

        if (!dw.isSigned() && sw.isSigned())  return false;

        return dw.bitWidth() > sw.bitWidth();

    }

    /**

     * Specialization of isNullConversion to reference types.

     * @param src the type of a stacked value

     * @param dst the reference type by which we'd like to treat it

     * @return whether the retyping can be done without a cast

     */

    public static boolean isNullReferenceConversion(Class<?> src, Class<?> dst) {

        assert(!dst.isPrimitive());

        if (dst.isInterface())  return true;   // verifier allows this

        if (isNullType(src))    return true;

        return dst.isAssignableFrom(src);

    }

    /**

     * Is the given type java.lang.Null or an equivalent null-only type?

     */

    public static boolean isNullType(Class<?> type) {

        if (type == null)  return false;

        return type == NULL_CLASS

            // This one may also be used as a null type.

            // TO DO: Decide if we really want to legitimize it here.

            // Probably we do, unless java.lang.Null really makes it into Java 7

            //|| type == Void.class

            // Locally known null-only class:

            || type == Empty.class

            ;

    }

    private static final Class<?> NULL_CLASS;

    static {

        Class<?> nullClass = null;

        try {

            nullClass = Class.forName("java.lang.Null");

        } catch (ClassNotFoundException ex) {

            // OK, we'll cope

        }

        NULL_CLASS = nullClass;

    }

    /**

     * True if a method handle can receive a call under a slightly different

     * method type, without moving or reformatting any stack elements.

     *

     * @param call the type of call being made

     * @param recv the type of the method handle receiving the call

     * @return whether the retyping can be done without motion or reformatting

     */

    public static boolean isNullConversion(MethodType call, MethodType recv) {

        if (call == recv)  return true;

        int len = call.parameterCount();

        if (len != recv.parameterCount())  return false;

        for (int i = 0; i < len; i++)

            if (!isNullConversion(call.parameterType(i), recv.parameterType(i)))

                return false;

        return isNullConversion(recv.returnType(), call.returnType());

    }

    /**

     * Determine if the JVM verifier allows a value of type call to be

     * passed to a formal parameter (or return variable) of type recv.

     * Returns 1 if the verifier allows the types to match without conversion.

     * Returns -1 if the types can be made to match by a JVM-supported adapter.

     * Cases supported are:

     * <ul><li>checkcast

     * </li><li>conversion between any two integral types (but not floats)

     * </li><li>unboxing from a wrapper to its corresponding primitive type

     * </li><li>conversion in either direction between float and double

     * </li></ul>

     * (Autoboxing is not supported here; it must be done via Java code.)

     * Returns 0 otherwise.

     */

    public static int canPassUnchecked(Class<?> src, Class<?> dst) {

        if (src == dst)

            return 1;

        if (dst.isPrimitive()) {

            if (dst == void.class)

                // Return anything to a caller expecting void.

                // This is a property of the implementation, which links

                // return values via a register rather than via a stack push.

                // This makes it possible to ignore cleanly.

                return 1;

            if (src == void.class)

                return 0;  // void-to-something?

            if (!src.isPrimitive())

                // Cannot pass a reference to any primitive type (exc. void).

                return 0;

            Wrapper sw = Wrapper.forPrimitiveType(src);

            Wrapper dw = Wrapper.forPrimitiveType(dst);

            if (sw.isSubwordOrInt() && dw.isSubwordOrInt()) {

                if (sw.bitWidth() >= dw.bitWidth())

                    return -1;   // truncation may be required

                if (!dw.isSigned() && sw.isSigned())

                    return -1;   // sign elimination may be required

                return 1;

            }

            if (src == float.class || dst == float.class) {

                if (src == double.class || dst == double.class)

                    return -1;   // floating conversion may be required

                else

                    return 0;    // other primitive conversions NYI

            } else {

                // all fixed-point conversions are supported

                return 0;

            }

        } else if (src.isPrimitive()) {

            // Cannot pass a primitive to any reference type.

            // (Maybe allow null.class?)

            return 0;

        }

        // Handle reference types in the rest of the block:

        // The verifier treats interfaces exactly like Object.

        if (isNullReferenceConversion(src, dst))

            // pass any reference to object or an arb. interface

            return 1;

        // else it's a definite "maybe" (cast is required)

        return -1;

    }

    public static boolean isSpreadArgType(Class<?> spreadArg) {

        return spreadArg.isArray();

    }

    public static Class<?> spreadArgElementType(Class<?> spreadArg, int i) {

        return spreadArg.getComponentType();

    }

}