/*
 * Copyright (C) 2008, Shawn O. Pearce <spearce@spearce.org>
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.eclipse.jgit.util;


/** Conversion utilities for network byte order handling. */
public final class NB {
	/**
	 * Compare a 32 bit unsigned integer stored in a 32 bit signed integer.
	 * <p>
	 * This function performs an unsigned compare operation, even though Java
	 * does not natively support unsigned integer values. Negative numbers are
	 * treated as larger than positive ones.
	 *
	 * @param a
	 *            the first value to compare.
	 * @param b
	 *            the second value to compare.
	 * @return < 0 if a < b; 0 if a == b; > 0 if a > b.
	 */
	public static int compareUInt32(final int a, final int b) {
		final int cmp = (a >>> 1) - (b >>> 1);
		if (cmp != 0)
			return cmp;
		return (a & 1) - (b & 1);
	}

	/**
	 * Convert sequence of 2 bytes (network byte order) into unsigned value.
	 *
	 * @param intbuf
	 *            buffer to acquire the 2 bytes of data from.
	 * @param offset
	 *            position within the buffer to begin reading from. This
	 *            position and the next byte after it (for a total of 2 bytes)
	 *            will be read.
	 * @return unsigned integer value that matches the 16 bits read.
	 */
	public static int decodeUInt16(final byte[] intbuf, final int offset) {
		int r = (intbuf[offset] & 0xff) << 8;
		return r | (intbuf[offset + 1] & 0xff);
	}

	/**
	 * Convert sequence of 4 bytes (network byte order) into signed value.
	 *
	 * @param intbuf
	 *            buffer to acquire the 4 bytes of data from.
	 * @param offset
	 *            position within the buffer to begin reading from. This
	 *            position and the next 3 bytes after it (for a total of 4
	 *            bytes) will be read.
	 * @return signed integer value that matches the 32 bits read.
	 */
	public static int decodeInt32(final byte[] intbuf, final int offset) {
		int r = intbuf[offset] << 8;

		r |= intbuf[offset + 1] & 0xff;
		r <<= 8;

		r |= intbuf[offset + 2] & 0xff;
		return (r << 8) | (intbuf[offset + 3] & 0xff);
	}

	/**
	 * Convert sequence of 4 bytes (network byte order) into unsigned value.
	 *
	 * @param intbuf
	 *            buffer to acquire the 4 bytes of data from.
	 * @param offset
	 *            position within the buffer to begin reading from. This
	 *            position and the next 3 bytes after it (for a total of 4
	 *            bytes) will be read.
	 * @return unsigned integer value that matches the 32 bits read.
	 */
	public static long decodeUInt32(final byte[] intbuf, final int offset) {
		int low = (intbuf[offset + 1] & 0xff) << 8;
		low |= (intbuf[offset + 2] & 0xff);
		low <<= 8;

		low |= (intbuf[offset + 3] & 0xff);
		return ((long) (intbuf[offset] & 0xff)) << 24 | low;
	}

	/**
	 * Convert sequence of 8 bytes (network byte order) into unsigned value.
	 *
	 * @param intbuf
	 *            buffer to acquire the 8 bytes of data from.
	 * @param offset
	 *            position within the buffer to begin reading from. This
	 *            position and the next 7 bytes after it (for a total of 8
	 *            bytes) will be read.
	 * @return unsigned integer value that matches the 64 bits read.
	 */
	public static long decodeUInt64(final byte[] intbuf, final int offset) {
		return (decodeUInt32(intbuf, offset) << 32)
				| decodeUInt32(intbuf, offset + 4);
	}

	/**
	 * Write a 16 bit integer as a sequence of 2 bytes (network byte order).
	 *
	 * @param intbuf
	 *            buffer to write the 2 bytes of data into.
	 * @param offset
	 *            position within the buffer to begin writing to. This position
	 *            and the next byte after it (for a total of 2 bytes) will be
	 *            replaced.
	 * @param v
	 *            the value to write.
	 */
	public static void encodeInt16(final byte[] intbuf, final int offset, int v) {
		intbuf[offset + 1] = (byte) v;
		v >>>= 8;

		intbuf[offset] = (byte) v;
	}

	/**
	 * Write a 32 bit integer as a sequence of 4 bytes (network byte order).
	 *
	 * @param intbuf
	 *            buffer to write the 4 bytes of data into.
	 * @param offset
	 *            position within the buffer to begin writing to. This position
	 *            and the next 3 bytes after it (for a total of 4 bytes) will be
	 *            replaced.
	 * @param v
	 *            the value to write.
	 */
	public static void encodeInt32(final byte[] intbuf, final int offset, int v) {
		intbuf[offset + 3] = (byte) v;
		v >>>= 8;

		intbuf[offset + 2] = (byte) v;
		v >>>= 8;

		intbuf[offset + 1] = (byte) v;
		v >>>= 8;

		intbuf[offset] = (byte) v;
	}

	/**
	 * Write a 64 bit integer as a sequence of 8 bytes (network byte order).
	 *
	 * @param intbuf
	 *            buffer to write the 48bytes of data into.
	 * @param offset
	 *            position within the buffer to begin writing to. This position
	 *            and the next 7 bytes after it (for a total of 8 bytes) will be
	 *            replaced.
	 * @param v
	 *            the value to write.
	 */
	public static void encodeInt64(final byte[] intbuf, final int offset, long v) {
		intbuf[offset + 7] = (byte) v;
		v >>>= 8;

		intbuf[offset + 6] = (byte) v;
		v >>>= 8;

		intbuf[offset + 5] = (byte) v;
		v >>>= 8;

		intbuf[offset + 4] = (byte) v;
		v >>>= 8;

		intbuf[offset + 3] = (byte) v;
		v >>>= 8;

		intbuf[offset + 2] = (byte) v;
		v >>>= 8;

		intbuf[offset + 1] = (byte) v;
		v >>>= 8;

		intbuf[offset] = (byte) v;
	}

	private NB() {
		// Don't create instances of a static only utility.
	}
}