Copyright (c) 2000, 2009 IBM Corporation and others.
This program and the accompanying materials
are made available under the terms of the Eclipse Public License 2.0
which accompanies this distribution, and is available at
https://www.eclipse.org/legal/epl-2.0/
SPDX-License-Identifier: EPL-2.0
Contributors:
    IBM Corporation - initial API and implementation
/*******************************************************************************
 * Copyright (c) 2000, 2009 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jdt.internal.core.util;

Abstract class that defines helpers methods for decoding .class file.
/**
 * Abstract class that defines helpers methods for decoding .class file.
 */
public abstract class ClassFileStruct {

	protected double doubleAt(byte[] reference, int relativeOffset, int structOffset) {
		return (Double.longBitsToDouble(i8At(reference, relativeOffset, structOffset)));
	}

	protected float floatAt(byte[] reference, int relativeOffset, int structOffset) {
		return (Float.intBitsToFloat(i4At(reference, relativeOffset, structOffset)));
	}
	protected int i1At(byte[] reference, int relativeOffset, int structOffset) {
		return reference[relativeOffset + structOffset];
	}
	protected int i2At(byte[] reference, int relativeOffset, int structOffset) {
		int position = relativeOffset + structOffset;
		return (reference[position++] << 8) + (reference[position] & 0xFF);
	}
	protected int i4At(byte[] reference, int relativeOffset, int structOffset) {
		int position = relativeOffset + structOffset;
		return ((reference[position++] & 0xFF) << 24)
			+ ((reference[position++] & 0xFF) << 16)
			+ ((reference[position++] & 0xFF) << 8)
			+ (reference[position] & 0xFF);
	}
	protected long i8At(byte[] reference, int relativeOffset, int structOffset) {
		int position = relativeOffset + structOffset;
		return (((long) (reference[position++] & 0xFF)) << 56)
						+ (((long) (reference[position++] & 0xFF)) << 48)
						+ (((long) (reference[position++] & 0xFF)) << 40)
						+ (((long) (reference[position++] & 0xFF)) << 32)
						+ (((long) (reference[position++] & 0xFF)) << 24)
						+ (((long) (reference[position++] & 0xFF)) << 16)
						+ (((long) (reference[position++] & 0xFF)) << 8)
						+ (reference[position++] & 0xFF);
	}

	protected int u1At(byte[] reference, int relativeOffset, int structOffset) {
		return (reference[relativeOffset + structOffset] & 0xFF);
	}
	protected int u2At(byte[] reference, int relativeOffset, int structOffset) {
		int position = relativeOffset + structOffset;
		return ((reference[position++] & 0xFF) << 8) + (reference[position] & 0xFF);
	}
	protected long u4At(byte[] reference, int relativeOffset, int structOffset) {
		int position = relativeOffset + structOffset;
		return (
			((reference[position++] & 0xFFL) << 24)
				+ ((reference[position++] & 0xFF) << 16)
				+ ((reference[position++] & 0xFF) << 8)
				+ (reference[position] & 0xFF));
	}
	protected char[] utf8At(byte[] reference, int relativeOffset, int structOffset, int bytesAvailable) {
		int length = bytesAvailable;
		char outputBuf[] = new char[bytesAvailable];
		int outputPos = 0;
		int readOffset = structOffset + relativeOffset;

		while (length != 0) {
			int x = reference[readOffset++] & 0xFF;
			length--;
			if ((0x80 & x) != 0) {
				if ((x & 0x20) != 0) {
					length-=2;
					x = ((x & 0xF) << 12) + ((reference[readOffset++] & 0x3F) << 6) + (reference[readOffset++] & 0x3F);
				} else {
					length--;
					x = ((x & 0x1F) << 6) + (reference[readOffset++] & 0x3F);
				}
			}
			outputBuf[outputPos++] = (char) x;
		}

		if (outputPos != bytesAvailable) {
			System.arraycopy(outputBuf, 0, (outputBuf = new char[outputPos]), 0, outputPos);
		}
		return outputBuf;
	}

	final boolean equals(char[] first, char[] second) {
		if (first == second)
			return true;
		if (first == null || second == null)
			return false;
		if (first.length != second.length)
			return false;

		for (int i = first.length; --i >= 0;)
			if (first[i] != second[i])
				return false;
		return true;
	}
}