Hello,

 

B= map bitAnd: 7.

M= map bitShift: -3.

 

All the best,

 

Ron Teitelbaum

 

 

From: squeak-dev-bounces at lists.squeakfoundation.org [mailto:squeak-dev-bounces at lists.squeakfoundation.org] On Behalf Of gettimothy
Sent: Tuesday, February 11, 2014 9:06 PM
To: The general-purpose Squeak developers list
Subject: [squeak-dev] for the operation MAP := B bitOr:( M bitShift:3) given MAP how do I derive B and M?

 

To reverse a MorphicEvent into an primitive event I need to unmap the buttons and modifiers.
In a primitive event, the fifth element (buttons) can be 1,2 or 4 and the sixth element (modifiers)  1,2,4 or 8.

HandMorph >> generateMouseEvent combines them into one field as such:



    buttons := evtBuf fifth.
    modifiers := evtBuf sixth.
    buttons := buttons bitOr: (modifiers bitShift: 3).


I need to reverse that   "buttons bitOr: (modifiers bitShift: 3)" back into the original values to recreate the primitive event.
Here are the possible values of B(uttons) and M(odifiers) under that operation:


B           M                 MAP
1 bitOr:(1 bitShift:3 ) 9
1 bitOr:(2 bitShift:3 ) 17
1 bitOr:(4 bitShift:3 ) 33
1 bitOr:(8 bitShift:3 ) 65


2 bitOr:(1 bitShift:3 )  10
2 bitOr:(2 bitShift:3 )  18
2 bitOr:(4 bitShift:3 )  34
2 bitOr:(8 bitShift:3 )  66


4 bitOr:(1 bitShift:3 )   12
4 bitOr:(2 bitShift:3 )   20
4 bitOr:(4 bitShift:3 )   36
4 bitOr:(8 bitShift:3 )   68

So, given a MAP on the right, I need to derive a B and a M.

I can figure something out, but it will probably be ugly. Hence, this email to the list.
Any bit-fiddlers on the board who know an elegant method?

thx.

tty.

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