Need help converting Hex to Long / Reading file contents at binary level

I'm trying to read consecutive bytes to a long variable.

BACKGROUND
I have code that can do this on a file. However this code is too slow for me as each file usually needs multiple reads. So I decided I could greatly speed this up by reading each file once into an array then searching the array instead. So I needed code that can do this conversion on an array instead.

And this is what I came up with:

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THE PROBLEM
But there's a catch. Before ditching the original code and replacing with my shiny new function, I decided to test a few thousand files with both methods to see whether they return the same result.

I tested over 3,000 files. And both methods returned the same result for every file tested...except three.

My new function does NOT return the correct value for these three files.

So I am looking for any forum user who has experience with reading files / converting Hex to Long. I am hoping he/she can help me work out why my function falls over on these files.

(I cant upload the files however I can provide the hex values at the exact point where the functions differ - I will do this in the next post)

Per the OP - I am uploading the details of the three files which I will refer to from now on as File01, File06 and File09.

I have provided for each file:

1. the read position at which the first variance occurs
2. the long result (aka Header) for each method (class is the original method, NEW = my new function)
3. the hex values for four bytes from the read position onwards

File01
09:28:49 class method - position(base0):=5357 Header:=101118975
09:28:49 NEW method - position(base0):=5357 Header:=6747135

Hex Values (starting from this position): FF F3 06 06


File06
09:28:49 class method - position(base0):=5478 Header:=285671167
09:28:49 NEW method - position(base0):=5478 Header:=18284287

Hex Values (starting from this position): FF FE 06 11


File09
09:28:49 class method - position(base0):=5614 Header:=-503120385
09:28:49 NEW method - position(base0):=5614 Header:=237174271

Hex Values (starting from this position): FF FD 02 E2


Optional - In case it helps - Further background on what I am doing: http://www.excelforum.com/excel-prog...his-works.html

I am thinking I can improve the response rate of this thread if I upload a workbook to demonstrate the problem. See attached workbook - you can run it on any file you like.

For the purpose of this test I will be using one of the sample pictures that come with Windows 7.

If I run the workbook on Koala.jpg at position 0 I get results of -520103681 for both methods.

If I run the workbook on Koala.jpg at position 255 I get two different results. Why?

Originally Posted by mc84excel

I am thinking I can improve the response rate of this thread if I upload a workbook to demonstrate the problem....

Aha..., you finally got the password
To be honest, if I opened a thread, and I just saw just a bunch of words or just screenshots, I immediately hit the x button on the upper right corner of this tab on my browser.


The problem of your function is at :

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Hex(avarBuffer(lngReadPos + something))
So lets say the value of avarBuffer is 10, return of Hex(10) is just "A", but actually you need "0A" (with leading zero)



So your code should be like :

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But, then again, you are "in hurry mode" (processing thousand of files), so why use multiple steps to convert the array to string first (using hex function), and then convert this string back to long ?
We know string operation is much longer than arithmetic operation.
So, you can use this function instead :

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Test speed file :
EF1096752b.xls



Regards

Originally Posted by karedog

Aha..., you finally got the password
To be honest, if I opened a thread, and I just saw just a bunch of words or just screenshots, I immediately hit the x button on the upper right corner of this tab on my browser.

Heh Without mentioning names I know one forum user who takes the opposite view - if he sees the thread contains a few words and an attached workbook, he wont bother looking further!

Originally Posted by karedog

So lets say the value of avarBuffer is 10, return of Hex(10) is just "A", but actually you need "0A" (with leading zero)

:slaps forehead: so that's the problem. Thank you very much karedog :reps:

I am very impressed that you not only identified the problem but you also provided a working function.

And as if that wasn't enough, you provided an alternative version of the function which you claim is even faster!
(I haven't speed tested them against one another yet. When I get to another computer with the main project on it - I will try them both out and eventually post the results back to this thread)

@ karedog
LOL Probably not You see the most I was hoping for was for someone to tell me where I was going wrong.

And one of my pet peeves is when I solve someones thread and they just say 'thanks' (sometimes not even that) and worse - they cant be bothered to spend one second to rep you.