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A question about 'Words'

Posted on 1998-10-28
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Last Modified: 2010-04-16
Hi,

I'm wondering if someone could give me an example of how I can divide a memory word containing the binary representation of an integer into fields of four bits and have each field represent a queue element.Also, how would I decompose an integer into an array of 4 bit integers using MOD and DIV? My text has absolutely no information regarding this and it's becoming frustrating.

I'm barely starting learning this so any help would be appreciated.

Best regards,

Pyramid
 
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Question by:Pyramid
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by:scrapdog
ID: 1215868
How is the word stored?  As an actual word or as a string of 0s and 1s?

Do you want everything to be represented in binary (0s and 1s) using strings?
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rwilson032697 earned 50 total points
ID: 1215869
Assuming by word you mean an unsigned 16 bit integer then you do it like this (in pascal - assuming array element 0 is in the most significant four bits of the word):

function GetArrayItemFromWord(ArrayWord : Word; Index : Integer) : Integer;

begin
  GetArrayItemFromWord := (ArrayWord AND ($F000 SHR (Index - 1) * 4)) SHR  (Index - 1) * 4;
end;

or using DIV and MOD

function GetArrayItemFromWord(ArrayWord : Word; Index : Integer) : Integer;

begin
  GetArrayItemFromWord := (ArrayWord DIV ($1000 SHR (Index - 1) * 4)) MOD $10;
end;

I leave the remaining exercise of applying this technique to represent a queue to your homework (hint each field will most likely be used as an index (1 to 15)).

Cheers,

Raymond.
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by:rwilson032697
ID: 1215870
Oops - Some corrections...

Proposed Answer
    From: rwilson
                                                                 Date: Wednesday, October 28 1998 - 05:20PM PST

    Assuming by word you mean an unsigned 16 bit integer then you do it like this (in pascal - assuming array element 0
    is in the most significant four bits of the word):

    function GetArrayItemFromWord(ArrayWord : Word; Index : Integer) : Integer;

    begin
      GetArrayItemFromWord := (ArrayWord AND ($F000 SHR (Index * 4))) SHR  (Index * 4);
    end;

    or using DIV and MOD

    function GetArrayItemFromWord(ArrayWord : Word; Index : Integer) : Integer;

    begin
      GetArrayItemFromWord := (ArrayWord DIV ($1000 SHR (Index * 4))) MOD $10;
    end;

Raymond.
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Expert Comment

by:vikiing
ID: 1215871
I think you need to get that integer divided into four groups of 4 bits each. I believe this is the simples way:

Var
     g1, g2, g3, g4: integer;  ('byte' or 'shortint' can serve)
     n: integer;
Begin
     n:=x   <--   'x' is the integer you wanna divide
     g1:=n and 15;  n:=n shr 4;
     g2:=n and 15;  n:=n shr 4;
     g3:=n and 15;  n:=n shr 4;
     g4:=n and 15;

The operation of "and"-ing leaves the lower 4 bits of "n", putting them at g1. After that, "n" is shifted to right 4 places, getting rid of the older bits, and putting the following 4 bits at rightmost position. Once again, g2 takes those bits; and the same for g3 and g4.

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Author Comment

by:Pyramid
ID: 1215872
Hi,
Sorry about not replying quickly. The information has helped greatly.

Thanks!!

Pyramid
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