NB.java

/*
 * Copyright (C) 2008, 2015 Shawn O. Pearce <spearce@spearce.org> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

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 &lt; 0 if a &lt; b; 0 if a == b; &gt; 0 if a &gt; 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);
    }

    /**
     * Compare a 64 bit unsigned integer stored in a 64 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 &lt; 0 if a &lt; b; 0 if a == b; &gt; 0 if a &gt; b.
     * @since 4.3
     */
    public static int compareUInt64(final long a, final long b) {
        long cmp = (a >>> 1) - (b >>> 1);
        if (cmp > 0) {
            return 1;
        } else if (cmp < 0) {
            return -1;
        }
        cmp = ((a & 1) - (b & 1));
        if (cmp > 0) {
            return 1;
        } else if (cmp < 0) {
            return -1;
        } else {
            return 0;
        }
    }

    /**
     * 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 3 bytes (network byte order) into unsigned value.
     *
     * @param intbuf
     *            buffer to acquire the 3 bytes of data from.
     * @param offset
     *            position within the buffer to begin reading from. This
     *            position and the next 2 bytes after it (for a total of 3
     *            bytes) will be read.
     * @return signed integer value that matches the 24 bits read.
     * @since 4.9
     */
    public static int decodeUInt24(byte[] intbuf, int offset) {
        int r = (intbuf[offset] & 0xff) << 8;
        r |= intbuf[offset + 1] & 0xff;
        return (r << 8) | (intbuf[offset + 2] & 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 8 bytes (network byte order) into signed 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 signed integer value that matches the 64 bits read.
     * @since 3.0
     */
    public static long decodeInt64(final byte[] intbuf, final int offset) {
        long r = intbuf[offset] << 8;

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

        r |= intbuf[offset + 2] & 0xff;
        r <<= 8;

        r |= intbuf[offset + 3] & 0xff;
        r <<= 8;

        r |= intbuf[offset + 4] & 0xff;
        r <<= 8;

        r |= intbuf[offset + 5] & 0xff;
        r <<= 8;

        r |= intbuf[offset + 6] & 0xff;
        return (r << 8) | (intbuf[offset + 7] & 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 24 bit integer as a sequence of 3 bytes (network byte order).
     *
     * @param intbuf
     *            buffer to write the 3 bytes of data into.
     * @param offset
     *            position within the buffer to begin writing to. This position
     *            and the next 2 bytes after it (for a total of 3 bytes) will be
     *            replaced.
     * @param v
     *            the value to write.
     * @since 4.9
     */
    public static void encodeInt24(byte[] intbuf, int offset, int v) {
        intbuf[offset + 2] = (byte) v;
        v >>>= 8;

        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 8 bytes 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.
    }
}