imap_utf7_decode

I can't find method for converting imap utf7 into utf8.
So I have to write several lines of code to solve this issue. May be this could be usefull. Here is no error handling but it could be added.
Usage:
$imap_utf7 = '[Gmail]/&BBIEMAQ2BD0EPgQ1-';
$utf8 = ImapUtf7::decode($imap_utf7);
$imap_utf7_2 = ImapUtf7::encode($utf8);
[ImapUtf7.php]
<?php
class ImapUtf7 {
 static $imap_base64 =
 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,';
 static private function encode_b64imap($s) { 
 $a=0; $al=0; $res=''; $n=strlen($s);
 for($i=0;$i<$n;$i++) {
 $a=($a<<8)|ord($s[$i]); $al+=8;
 for(;$al>=6;$al-=6) $res.=self::$imap_base64[($a>>($al-6))&0x3F];
 }
 if ($al>0) { $res.=self::$imap_base64[($a<<(6-$al))&0x3F]; }
 return $res;
 }
 static private function encode_utf8_char($w) {
 if ($w&0x80000000) return '';
 if ($w&0xFC000000) $n=5; else
 if ($w&0xFFE00000) $n=4; else
 if ($w&0xFFFF0000) $n=3; else
 if ($w&0xFFFFF800) $n=2; else
 if ($w&0xFFFFFF80) $n=1; else return chr($w);
 $res=chr(( (255<<(7-$n)) | ($w>>($n*6)) )&255); 
 while(--$n>=0) $res.=chr((($w>>($n*6))&0x3F)|0x80);
 return $res;
 }
 static private function decode_b64imap($s) {
 $a=0; $al=0; $res=''; $n=strlen($s);
 for($i=0;$i<$n;$i++) {
 $k=strpos(self::$imap_base64,$s[$i]); if ($k===FALSE) continue;
 $a=($a<<6)|$k; $al+=6;
 if ($al>=8) { $res.=chr(($a>>($al-8))&255);$al-=8; }
 }
 $r2=''; $n=strlen($res);
 for($i=0;$i<$n;$i++) {
 $c=ord($res[$i]); $i++;
 if ($i<$n) $c=($c<<8) | ord($res[$i]);
 $r2.=self::encode_utf8_char($c);
 }
 return $r2;
 }
 static function encode($s) {
 $n=strlen($s);$err=0;$buf='';$res='';
 for($i=0;$i<$n;) {
 $x=ord($s[$i++]);
 if (($x&0x80)==0x00) { $r=$x;$w=0; } 
 else if (($x&0xE0)==0xC0) { $w=1; $r=$x &0x1F; } 
 else if (($x&0xF0)==0xE0) { $w=2; $r=$x &0x0F; } 
 else if (($x&0xF8)==0xF0) { $w=3; $r=$x &0x07; } 
 else if (($x&0xFC)==0xF8) { $w=4; $r=$x &0x03; } 
 else if (($x&0xFE)==0xFC) { $w=5; $r=$x &0x01; } 
 else if (($x&0xC0)==0x80) { $w=0; $r=-1; $err++; } 
 else { $w=0;$r=-2;$err++; }
 for($k=0;$k<$w && $i<$n; $k++) {
 $x=ord($s[$i++]); if ($x&0xE0!=0x80) { $err++; }
 $r=($r<<6)|($x&0x3F);
 }
 if ($r<0x20 || $r>0x7E ) {
 $buf.=chr(($r>>8)&0xFF); $buf.=chr($r&0xFF);
 } else {
 if (strlen($buf)) { 
 $res.='&'.self::encode_b64imap($buf).'-';
 $buf=''; 
 }
 if ($r==0x26) { $res.='&-'; } else $res.=chr($r);
 }
 }
 if (strlen($buf)) $res.='&'.self::encode_b64imap($buf).'-';
 return $res;
 }
 static function decode($s) {
 $res=''; $n=strlen($s); $h=0;
 while($h<$n) {
 $t=strpos($s,'&',$h); if ($t===false) $t=$n;
 $res.=substr($s,$h,$t-$h); $h=$t+1; if ($h>=$n) break;
 $t=strpos($s,'-',$h); if ($t===false) $t=$n;
 $k=$t-$h; 
 if ($k==0) $res.='&'; 
 else $res.=self::decode_b64imap(substr($s,$h,$k));
 $h=$t+1;
 }
 return $res;
 }
}

For "Outlook-style" UTF-7, you can also use:
mb_convert_encoding( $str, "ISO_8859-1", "UTF7-IMAP" ); # for decoding
mb_convert_encoding( $str, "UTF7-IMAP", "ISO_8859-1" ); # for encoding

For Chinese charset, we can use: 
mb_convert_encoding($mailbox, "UTF7-IMAP", "GB2312"); 
when you want to create a mailbox in Chinese. 
OR 
mb_convert_encoding($mailbox, "GB2312", "UTF7-IMAP");
when you want to show the listed mailbox with the right charset.