bugGNU MIX Development Kit - Bugs: bug #5652, Assembler shouldn't mask index...

 
 

bug #5652: Assembler shouldn't mask index field

Submitted by:  Joel Ray Holveck <joelh>
Submitted on:  Wed 01 Oct 2003 02:41:23 AM UTC  
 
Category: NoneSeverity: 3 - Normal
Item Group: NoneStatus: Fixed
Privacy: PublicAssigned to: Jose Antonio Ortega Ruiz <jao>
Open/Closed: Closed

Add a New Comment(Rich Markup)
   

You are not logged in

Please log in, so followups can be emailed to you.

 

Sun 10 Oct 2010 12:03:18 AM UTC, comment #1:

Sorry for the looooong delay. Fixed in Git and forthcoming 1.2.6 release.

Jose Antonio Ortega Ruiz <jao>
Project AdministratorIn charge of this item.
Wed 01 Oct 2003 02:41:23 AM UTC, original submission:

The assembler, in mix_ins_to_word (and mix_ins_to_word_uncheck) presently truncates the index field to three bits.

As far as I can tell, this serves no useful purpose. It doesn't restrict the index to valid index registers, since 7 is still passed. It doesn't restrict input, since index register values > 7 are modified to other values (which are pretty much useless), rather than generating an error. It isn't required to make a valid word, since an entire byte is available in the I field.

There's an old tradition on machines similar to the MIX (such as the PDP-4, IBM 360, etc) of holding data in unused portions of instructions, or (if you can wrangle it) used portions of instructions. Or, if you don't have anything useful to store, then your initials. ANDing the index field with 7 prevents this, and is unnecessary.

Joel Ray Holveck <joelh>

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach File(s):
   
   
Comment:
   

No files currently attached

 

Depends on the following items: None found

Items that depend on this one: None found

 

Carbon-Copy List
  • -unavailable- added by jao (Updated the item)
  •  

    Do you think this task is very important?
    If so, you can click here to add your encouragement to it.
    This task has 0 encouragements so far.

    Only logged-in users can vote.

     

    Please enter the title of George Orwell's famous dystopian book (it's a date):

     

     

    Follow 5 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Sun 10 Oct 2010 12:03:18 AM UTCjaoStatusIn Progress=>Fixed
      Open/ClosedOpen=>Closed
    Mon 12 Apr 2010 06:12:11 AM UTCjaoAssigned toNone=>jao
    Mon 12 Apr 2010 06:12:10 AM UTCjaoStatusPostponed=>In Progress
    Mon 19 Sep 2005 08:12:00 PM UTCjaoStatusNone=>Postponed

    Back to the top


    Powered by Savane 3.1-cleanup1