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

	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.
	* <p>
	* If both types are references, we apply the verifier's subclass check
	* (or subtyping, if keepInterfaces).
	* If the src type is a type guaranteed to be null (Void) it can be converted
	* to any other reference type.
	* <p>
	* If both types are primitives, we apply the verifier's primitive conversions.
	* These do not include Java conversions such as long to double, since those
	* require computation and (in general) stack depth changes.
	* But very simple 32-bit viewing changes, such as byte to int,
	* are null conversions, because they do not require any computation.
	* These conversions are from any type to a wider type up to 32 bits,
	* as long as the conversion is not signed to unsigned (byte to char).
	* <p>
	* The primitive type 'void' does not interconvert with any other type,
	* even though it is legal to drop any type from the stack and "return void".
	* The stack effects, though are different between void and any other type,
	* so it is safer to report a non-trivial conversion.
	*
	* @param src the type of a stacked value
	* @param dst the type by which we'd like to treat it
	* @param keepInterfaces if false, we treat any interface as if it were Object
	* @return whether the retyping can be done without motion or reformatting
	*/
	public static boolean isNullConversion(Class<?> src, Class<?> dst, boolean keepInterfaces) {
	if (src == dst) return true;
	// Verifier allows any interface to be treated as Object:
	if (!keepInterfaces) {
	if (dst.isInterface()) dst = Object.class;
	if (src.isInterface()) src = Object.class;
	if (src == dst) return true; // check again
	}
	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) {
	// Any reference statically typed as Void is guaranteed to be null.
	// Therefore, it can be safely treated as a value of any
	// other type that admits null, i.e., a reference type.
	if (type == Void.class) return true;
	// Locally known null-only class:
	if (type == Empty.class) return true;
	return false;
	}

	/**
	* 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, boolean keepInterfaces) {
	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), keepInterfaces))
	return false;
	return isNullConversion(recv.returnType(), call.returnType(), keepInterfaces);
	}

	/**
	* 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();
	}
	}

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