<?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
*/
namespace lsolesen\pel;
/**
* Routines for converting back and forth between bytes and integers.
*
* @author Martin Geisler <mgeisler@users.sourceforge.net>
* @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 integer $value
* the unsigned short that will be converted. The lower
* two bytes will be extracted regardless of the actual size passed.
*
* @param boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}.
*
* @return string the bytes representing the unsigned short.
*/
public static function shortToBytes($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 integer $value
* the signed short that will be converted. The lower
* two bytes will be extracted regardless of the actual size passed.
*
* @param boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}.
*
* @return string the bytes representing the signed short.
*/
public static function sShortToBytes($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 integer $value
* 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 boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}.
*
* @return string the bytes representing the unsigned long.
*/
public static function longToBytes($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 integer $value
* 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 boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}.
*
* @return string the bytes representing the signed long.
*/
public static function sLongToBytes($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 $bytes
* the bytes.
*
* @param integer $offset
* The byte found at the offset will be
* returned as an integer. The must be at least one byte available
* at offset.
*
* @return integer $offset the unsigned byte found at offset, e.g., an integer
* in the range 0 to 255.
*/
public static function bytesToByte($bytes, $offset)
{
return ord($bytes[$offset]);
}
/**
* Extract a signed byte from bytes.
*
* @param string $bytes
* the bytes.
*
* @param integer $offset
* the offset. The byte found at the offset will be
* returned as an integer. The must be at least one byte available
* at offset.
*
* @return integer the signed byte found at offset, e.g., an integer in
* the range -128 to 127.
*/
public static function bytesToSByte($bytes, $offset)
{
$n = self::bytesToByte($bytes, $offset);
if ($n > 127) {
return $n - 256;
} else {
return $n;
}
}
/**
* Extract an unsigned short from bytes.
*
* @param string $bytes
* the bytes.
*
* @param integer $offset
* 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.
* @param boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}.
* @return integer the unsigned short found at offset, e.g., an integer
* in the range 0 to 65535.
*
*/
public static function bytesToShort($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 $bytes
*
* @param integer $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.
* @param boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}.
* @return integer the signed byte found at offset, e.g., an integer in
* the range -32768 to 32767.
*
*/
public static function bytesToSShort($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 $bytes
*
* @param integer $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.
* @param boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}.
* @return integer the unsigned long found at offset, e.g., an integer
* in the range 0 to 4294967295.
*
*/
public static function bytesToLong($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 $bytes
*
* @param integer $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.
* @param boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}. *
* @return integer the signed long found at offset, e.g., an integer in
* the range -2147483648 to 2147483647.
*
*/
public static function bytesToSLong($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 $bytes
*
* @param integer $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.
* @param boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}. *
* @return array the unsigned rational found at offset, e.g., an
* array with two integers in the range 0 to 4294967295.
*
*/
public static function bytesToRational($bytes, $offset, $endian)
{
return [
self::bytesToLong($bytes, $offset, $endian),
self::bytesToLong($bytes, $offset + 4, $endian)
];
}
/**
* Extract a signed rational from bytes.
*
* @param string $bytes
*
* @param integer $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.
* @param boolean $endian
* one of {@link LITTLE_ENDIAN} and {@link
* BIG_ENDIAN}.
* @return array the signed rational found at offset, e.g., an array
* with two integers in the range -2147483648 to 2147483647.
*
*/
public static function bytesToSRational($bytes, $offset, $endian)
{
return [
self::bytesToSLong($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 $bytes
* the bytes that will be dumped.
*
* @param integer $max
* the maximum number of bytes to dump. If this is left
* out (or left to the default of 0), then the entire string will be
* dumped.
* @return void
*/
public static function bytesToDump($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");
}
}