<?php

/**
 *  PEL: PHP Exif Library.  A library with support for reading and
 *  writing all Exif headers in JPEG and TIFF images using PHP.
 *
 *  Copyright (C) 2004, 2005  Martin Geisler.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program in the file COPYING; if not, write to the
 *  Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
 *  Boston, MA 02110-1301 USA
 */

/* $Id$ */


/**
 * Routines for converting back and forth between bytes and integers.
 *
 * @author Martin Geisler <mgeisler@users.sourceforge.net>
 * @version $Revision$
 * @date $Date$
 * @license http://www.gnu.org/licenses/gpl.html GNU General Public
 * License (GPL)
 * @package PEL
 */

/**
 * Conversion functions to and from bytes and integers.
 *
 * The functions found in this class are used to convert bytes into
 * integers of several sizes ({@link bytesToShort}, {@link
 * bytesToLong}, and {@link bytesToRational}) and convert integers of
 * several sizes into bytes ({@link shortToBytes} and {@link
 * longToBytes}).
 *
 * All the methods are static and they all rely on an argument that
 * specifies the byte order to be used, this must be one of the class
 * constants {@link LITTLE_ENDIAN} or {@link BIG_ENDIAN}.  These
 * constants will be referred to as the pseudo type PelByteOrder
 * throughout the documentation.
 *
 * @author Martin Geisler <mgeisler@users.sourceforge.net>
 * @package PEL
 */
class PelConvert {

    /**
     * Little-endian (Intel) byte order.
     *
     * Data stored in little-endian byte order store the least
     * significant byte first, so the number 0x12345678 becomes 0x78
     * 0x56 0x34 0x12 when stored with little-endian byte order.
     */
    const LITTLE_ENDIAN = true;

    /**
     * Big-endian (Motorola) byte order.
     *
     * Data stored in big-endian byte order store the most significant
     * byte first, so the number 0x12345678 becomes 0x12 0x34 0x56 0x78
     * when stored with big-endian byte order.
     */
    const BIG_ENDIAN = false;


    /**
     * Convert an unsigned short into two bytes.
     *
     * @param int the unsigned short that will be converted.  The lower
     * two bytes will be extracted regardless of the actual size passed.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     *
     * @return string the bytes representing the unsigned short.
     */
    static function shortToBytes($value, $endian) {
        if ($endian == self::LITTLE_ENDIAN)
        return chr($value) . chr($value >> 8);
        else
        return chr($value >> 8) . chr($value);
    }


    /**
     * Convert a signed short into two bytes.
     *
     * @param int the signed short that will be converted.  The lower
     * two bytes will be extracted regardless of the actual size passed.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     *
     * @return string the bytes representing the signed short.
     */
    static function sShortToBytes($value, $endian) {
        /* We can just use shortToBytes, since signed shorts fits well
         * within the 32 bit signed integers used in PHP. */
        return self::shortToBytes($value, $endian);
    }


    /**
     * Convert an unsigned long into four bytes.
     *
     * Because PHP limits the size of integers to 32 bit signed, one
     * cannot really have an unsigned integer in PHP.  But integers
     * larger than 2^31-1 will be promoted to 64 bit signed floating
     * point numbers, and so such large numbers can be handled too.
     *
     * @param int the unsigned long that will be converted.  The
     * argument will be treated as an unsigned 32 bit integer and the
     * lower four bytes will be extracted.  Treating the argument as an
     * unsigned integer means that the absolute value will be used.  Use
     * {@link sLongToBytes} to convert signed integers.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     *
     * @return string the bytes representing the unsigned long.
     */
    static function longToBytes($value, $endian) {
        /* We cannot convert the number to bytes in the normal way (using
         * shifts and modulo calculations) because the PHP operator >> and
         * function chr() clip their arguments to 2^31-1, which is the
         * largest signed integer known to PHP.  But luckily base_convert
         * handles such big numbers. */
        $hex = str_pad(base_convert($value, 10, 16), 8, '0', STR_PAD_LEFT);
        if ($endian == self::LITTLE_ENDIAN)
        return (chr(hexdec($hex{6} . $hex{7})) .
        chr(hexdec($hex{4} . $hex{5})) .
        chr(hexdec($hex{2} . $hex{3})) .
        chr(hexdec($hex{0} . $hex{1})));
        else
        return (chr(hexdec($hex{0} . $hex{1})) .
        chr(hexdec($hex{2} . $hex{3})) .
        chr(hexdec($hex{4} . $hex{5})) .
        chr(hexdec($hex{6} . $hex{7})));
    }


    /**
     * Convert a signed long into four bytes.
     *
     * @param int the signed long that will be converted.  The argument
     * will be treated as a signed 32 bit integer, from which the lower
     * four bytes will be extracted.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     *
     * @return string the bytes representing the signed long.
     */
    static function sLongToBytes($value, $endian) {
        /* We can convert the number into bytes in the normal way using
         * shifts and modulo calculations here (in contrast with
         * longToBytes) because PHP automatically handles 32 bit signed
         * integers for us. */
        if ($endian == self::LITTLE_ENDIAN)
        return (chr($value) .
        chr($value >>  8) .
        chr($value >> 16) .
        chr($value >> 24));
        else
        return (chr($value >> 24) .
        chr($value >> 16) .
        chr($value >>  8) .
        chr($value));
    }


    /**
     * Extract an unsigned byte from a string of bytes.
     *
     * @param string the bytes.
     *
     * @param int the offset.  The byte found at the offset will be
     * returned as an integer.  The must be at least one byte available
     * at offset.
     *
     * @return int the unsigned byte found at offset, e.g., an integer
     * in the range 0 to 255.
     */
    static function bytesToByte($bytes, $offset) {
        return ord($bytes{$offset});
    }


    /**
     * Extract a signed byte from bytes.
     *
     * @param string the bytes.
     *
     * @param int the offset.  The byte found at the offset will be
     * returned as an integer.  The must be at least one byte available
     * at offset.
     *
     * @return int the signed byte found at offset, e.g., an integer in
     * the range -128 to 127.
     */
    static function bytesToSByte($bytes, $offset) {
        $n = self::bytesToByte($bytes, $offset);
        if ($n > 127)
        return $n - 256;
        else
        return $n;
    }


    /**
     * Extract an unsigned short from bytes.
     *
     * @param string the bytes.
     *
     * @param int the offset.  The short found at the offset will be
     * returned as an integer.  There must be at least two bytes
     * available beginning at the offset given.
     *
     * @return int the unsigned short found at offset, e.g., an integer
     * in the range 0 to 65535.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     */
    static function bytesToShort($bytes, $offset, $endian) {
        if ($endian == self::LITTLE_ENDIAN)
        return (ord($bytes{$offset+1}) * 256 +
        ord($bytes{$offset}));
        else
        return (ord($bytes{$offset})   * 256 +
        ord($bytes{$offset+1}));
    }


    /**
     * Extract a signed short from bytes.
     *
     * @param string the bytes.
     *
     * @param int the offset.  The short found at offset will be returned
     * as an integer.  There must be at least two bytes available
     * beginning at the offset given.
     *
     * @return int the signed byte found at offset, e.g., an integer in
     * the range -32768 to 32767.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     */
    static function bytesToSShort($bytes, $offset, $endian) {
        $n = self::bytesToShort($bytes, $offset, $endian);
        if ($n > 32767)
        return $n - 65536;
        else
        return $n;
    }


    /**
     * Extract an unsigned long from bytes.
     *
     * @param string the bytes.
     *
     * @param int the offset.  The long found at offset will be returned
     * as an integer.  There must be at least four bytes available
     * beginning at the offset given.
     *
     * @return int the unsigned long found at offset, e.g., an integer
     * in the range 0 to 4294967295.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     */
    static function bytesToLong($bytes, $offset, $endian) {
        if ($endian == self::LITTLE_ENDIAN)
        return (ord($bytes{$offset+3}) * 16777216 +
        ord($bytes{$offset+2}) * 65536    +
        ord($bytes{$offset+1}) * 256      +
        ord($bytes{$offset}));
        else
        return (ord($bytes{$offset})   * 16777216 +
        ord($bytes{$offset+1}) * 65536    +
        ord($bytes{$offset+2}) * 256      +
        ord($bytes{$offset+3}));
    }


    /**
     * Extract a signed long from bytes.
     *
     * @param string the bytes.
     *
     * @param int the offset.  The long found at offset will be returned
     * as an integer.  There must be at least four bytes available
     * beginning at the offset given.
     *
     * @return int the signed long found at offset, e.g., an integer in
     * the range -2147483648 to 2147483647.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     */
    static function bytesToSLong($bytes, $offset, $endian) {
        $n = self::bytesToLong($bytes, $offset, $endian);
        if ($n > 2147483647)
        return $n - 4294967296;
        else
        return $n;
    }


    /**
     * Extract an unsigned rational from bytes.
     *
     * @param string the bytes.
     *
     * @param int the offset.  The rational found at offset will be
     * returned as an array.  There must be at least eight bytes
     * available beginning at the offset given.
     *
     * @return array the unsigned rational found at offset, e.g., an
     * array with two integers in the range 0 to 4294967295.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     */
    static function bytesToRational($bytes, $offset, $endian) {
        return array(self::bytesToLong($bytes, $offset, $endian),
        self::bytesToLong($bytes, $offset+4, $endian));
    }


    /**
     * Extract a signed rational from bytes.
     *
     * @param string the bytes.
     *
     * @param int the offset.  The rational found at offset will be
     * returned as an array.  There must be at least eight bytes
     * available beginning at the offset given.
     *
     * @return array the signed rational found at offset, e.g., an array
     * with two integers in the range -2147483648 to 2147483647.
     *
     * @param PelByteOrder one of {@link LITTLE_ENDIAN} and {@link
     * BIG_ENDIAN}.
     */
    static function bytesToSRational($bytes, $offset, $endian) {
        return array(self::bytesToSLong($bytes, $offset, $endian),
        self::bytesToSLong($bytes, $offset+4, $endian));
    }


    /**
     * Format bytes for dumping.
     *
     * This method is for debug output, it will format a string as a
     * hexadecimal dump suitable for display on a terminal.  The output
     * is printed directly to standard out.
     *
     * @param string the bytes that will be dumped.
     *
     * @param int the maximum number of bytes to dump.  If this is left
     * out (or left to the default of 0), then the entire string will be
     * dumped.
     */
    static function bytesToDump($bytes, $max = 0) {
        $s = strlen($bytes);

        if ($max > 0)
        $s = min($max, $s);

        $line = 24;

        for ($i = 0; $i < $s; $i++) {
            printf('%02X ', ord($bytes{$i}));

            if (($i+1) % $line == 0)
            print("\n");
        }
        print("\n");
    }

}

