Solved

Effective/quick algorithm for changing single chars in buffer

Posted on 1997-09-16
5
240 Views
Last Modified: 2010-04-04
I have a buffer of data (a web html page). I need to replace all occurences of eg char '100' with char '232'. I have 5 different chars all together to replace (eg. 34->33, 55->75,...).
I need a really effective algorithm for this. Delphi if good, assembler is better.
0
Comment
Question by:kolarb
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
5 Comments
 
LVL 12

Accepted Solution

by:
andrewjb earned 100 total points
ID: 1345035
How about this in assemler. It expects a PChar buffer ( terminated with a null character ) and 'change' and 'replace with' characters to swap.

If you've definitely got exactly 5 changes to make, you could do them all in one loop ( add another comment to this questions ), but that wouldn't be useful in the future ....


procedure Change( Buff : PChar ; FromChar , ToChar : char);
asm
@start:
  mov ch,[eax]
  test ch,ch              { Test for string end }
  jz @done

  cmp ch , dl             { Test for char to replace }
  jnz @Loop

  mov byte ptr [eax] , cl  { Replace with new char }
@loop:
  inc eax
  jmp @start

@done:
end;

0
 
LVL 2

Author Comment

by:kolarb
ID: 1345036
I have exactly five changes to make. I also know the exact length of the buffer. Can you incorporate that in the program?
0
 
LVL 2

Author Comment

by:kolarb
ID: 1345037
Make up the values for example purposes.
0
 
LVL 12

Expert Comment

by:andrewjb
ID: 1345038
Here you go :

( Replace the letters with character values if you want. e.g. 'a' could be replaced with 97 etc. )


To be honest, it wouldn't be too much slower in pascal.

procedure Change( Buff : PChar ; Length : integer );
asm
@start:
  test edx , edx
  jz @done

  mov cl,[eax]

@Exchange1:
  cmp cl , 'a'             { Test for char to replace }
  jnz @Exchange2
  mov byte ptr [eax] , 'b' { Replace with new char }

@Exchange2:
  cmp cl , 'e'             { Test for char to replace }
  jnz @Exchange3
  mov byte ptr [eax] , 'h' { Replace with new char }

@Exchange3:
  cmp cl , 'f'             { Test for char to replace }
  jnz @Exchange4
  mov byte ptr [eax] , 'l' { Replace with new char }

@Exchange4:
  cmp cl , 'r'             { Test for char to replace }
  jnz @Exchange5
  mov byte ptr [eax] , 'm' { Replace with new char }

@Exchange5:
  cmp cl , 'q'             { Test for char to replace }
  jnz @Loop
  mov byte ptr [eax] , 'z' { Replace with new char }


@loop:
  inc eax
  dec edx
  jmp @start

@done:
end;

0
 
LVL 2

Author Comment

by:kolarb
ID: 1345039
Thank you.
0

Featured Post

Free Tool: ZipGrep

ZipGrep is a utility that can list and search zip (.war, .ear, .jar, etc) archives for text patterns, without the need to extract the archive's contents.

One of a set of tools we're offering as a way to say thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

This article explains how to create forms/units independent of other forms/units object names in a delphi project. Have you ever created a form for user input in a Delphi project and then had the need to have that same form in a other Delphi proj…
Have you ever had your Delphi form/application just hanging while waiting for data to load? This is the article to read if you want to learn some things about adding threads for data loading in the background. First, I'll setup a general applica…
The Email Laundry PDF encryption service allows companies to send confidential encrypted  emails to anybody. The PDF document can also contain attachments that are embedded in the encrypted PDF. The password is randomly generated by The Email Laundr…

733 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question