BIT Operators VB6 and PHP

Following on from a related question at https://www.experts-exchange.com/questions/27303952/VB6-to-PHP-Code-Checksum.html

I have now a simple (not required to be 'tricky' or foolproof) key creator that I've put together in VB6 and have been using on my software for a number of years now. I have been trying to simulate that algorithm in PHP to generate the same 'key' so users can generate the access key online, instead of having to ring me.

The trick I'm finding is the codes are producing different keys. This may be related to how PHP and VB6 handle Bit Operators.

I've attached the code on both PHP and VB6.

Given an input string of say "1234-123-123-123JOE BLOW" the output in VB6 is 03FCGGFB, whilst the PHP output is 0017GD02

I've played a bit with the PHP code to try different things.

Any ideas would be great.

Public Function gencheck(sstring As String) As String
   
    Dim I As Integer
    Dim chk As Long
    Dim n1, n2, n3, n4, n5, n6, n7, n8 As Byte
    
    chk = 0
    For I = 1 To Len(sstring)
        chk = chk * 2
        
        ' Set bit 0 to whatever bit 16 is..
        If (chk And 65536) = 0 Then
            ' Bit 16 is clear, so clear bit 0
            chk = chk And 65534
        Else
            ' Bit 16 is set, so set bit 0
            chk = chk Or 1
        End If
        ' Clear bit 16..
        chk = chk And 65535
        
        ' XOR sum
        chk = chk Xor Asc(Mid$(sstring, I, 1))
    Next I
    
   
    ' We have the additive checksum, so now get the 4 nybbles..
    n8 = chk And 15
    chk = Int(chk / 4)
    n7 = chk And 15
    chk = Int(chk / 4)
    n6 = chk And 15
    chk = Int(chk / 4)
    n5 = chk And 15
    chk = Int(chk / 4)
    n4 = chk And 15
    chk = Int(chk / 4)
    n3 = chk And 15
    chk = Int(chk / 4)
    n2 = chk And 15
    chk = Int(chk / 4)
    n1 = chk And 15
    
    ' Add 48 to each one (ascii '0')
    n1 = n1 + 48
    
    If n1 > 57 Then
        n1 = 65 + (n1 - 57)
    End If
    
    n2 = n2 + 48
    
    If n2 > 57 Then
        n2 = 65 + (n2 - 57)
    End If
    
    n3 = n3 + 48
    
    If n3 > 57 Then
        n3 = 65 + (n3 - 57)
    End If
    
    n4 = n4 + 48
    If n4 > 57 Then
        n4 = 65 + (n4 - 57)
    End If
    
    n5 = n5 + 48
    If n5 > 57 Then
        n5 = 65 + (n5 - 57)
    End If
    
    n6 = n6 + 48
    If n6 > 57 Then
        n6 = 65 + (n6 - 57)
    End If
    
    n7 = n7 + 48
    If n7 > 57 Then
        n7 = 65 + (n7 - 57)
    End If
    
    n8 = n8 + 48
    If n8 > 57 Then
        n8 = 65 + (n8 - 57)
    End If
       
    gencheck = Chr$(n1) + Chr$(n2) + Chr$(n3) + Chr$(n4) + Chr$(n5) + Chr$(n6) + Chr$(n7) + Chr$(n8)
End Function

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function getchecksum($sstring){
	    $chk = 0;
	    $len = strlen($sstring);	
	    for ($I=1; $I<=$len; $I++){
	        $chk = $chk * 2;
	        // Set bit 0 to whatever bit 16 is..
	        If (($chk & 65536) == 0 ){
	            // Bit 16 is clear, so clear bit 0
	            $chk = ($chk & 65534);
	        } else {
	            // Bit 16 is set, so set bit 0
	            $chk = ($chk Or 1);
	        }
	        // Clear bit 16..
	        $chk = ($chk & 65535);
	        
	        // XOR sum
	        $chk = ($chk ^ Ord(substr($sstring, $I, 1)));
	    }
	    
	    $n8 = ($chk & 15);
	    $chk = intval($chk / 4);
	    $n7 = ($chk & 15);
	    $chk = intval($chk / 4);
	    $n6 = ($chk & 15);
	    $chk = intval($chk / 4);
	    $n5 = ($chk & 15);
	    $chk = intval($chk / 4);
	    $n4 = ($chk & 15);
	    $chk = intval($chk / 4);
	    $n3 = ($chk & 15);
	    $chk = intval($chk / 4);
	    $n2 = ($chk & 15);
	    $chk = intval($chk / 4);
	    $n1 = ($chk & 15);
	    
	    // Add 48 to each one (ascii '0')
	    $n1 = $n1 + 48;
	    
	    If ( $n1 > 57 ){
	        $n1 = 65 + ($n1 - 57);
	    }
	    
	    $n2 = $n2 + 48;
	    
	    If ( $n2 > 57 ){
	        $n2 = 65 + ($n2 - 57);
	    }
	    
	    $n3 = $n3 + 48;
	    
	    If ( $n3 > 57 ){
	       $n3 = 65 + ($n3 - 57);
	    }
	    
	    $n4 = $n4 + 48;
	    If ($n4 > 57){
	        $n4 = 65 + ($n4 - 57);
	    }
	    
	    $n5 = $n5 + 48;
	    If ($n5 > 57){
	        $n5 = 65 + ($n5 - 57);
	    }
	    
	    $n6 = $n6 + 48;
	    If ($n6 > 57){
	        $n6 = 65 + ($n6 - 57);
	    }
	    
	    $n7 = $n7 + 48;
	    If ($n7 > 57){
	        $n7 = 65 + ($n7 - 57);
	    }
	    
	    $n8 = $n8 + 48;
	    If ($n8 > 57 ){
	        $n8 = 65 + ($n8 - 57);
	    }

	    return chr($n1).chr($n2).chr($n3).chr($n4).chr($n5).chr($n6).chr($n7).chr($n8);
	}

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