Calculate a Checksum

[youssef]

Hi,

I would like to create a function to calculate a checksum for a arraydata.

But I don't understand what I want for this checksum :

" lower 8 bits of the sum from data1 to data10 equals to zero".

My english is not perfect but I understand the sum of the data1 to data10 but equals to zero, I don't understand.

Best regards

 

[cluelessC]

Hi, there!
What does "lower 8 bits" mean? I am not quite clear on what it is exactly that you need to do, but could it be that you are asked to initialise the first 8 elements to zero first?
If so, then in Borland C++Builder that would look something like this:
int i = 0; //initialise index
int DataArray[10]; //declare your array (if
//your data consists of integers
while (i < 8)
{
DataArray = 0;
i = i + 1;
}
I hope I got the question right? And I'm sorry if that's not what is expected - I'm only a beginner myself!
CluelessC.

 

[vkavith]

I did something like this for a group of byte elements. See if u can convert this to yr array

UNSIGNED32 seed = 0x746d7361;
UNSIGNED32 i, icVal0 = seed, icVal1 = 0;
BYTE* pg = *ptrToBeginningOfArray;
for (i = 0; i < numBytes; i++, pg++)
{
icVal0 += *pg;
icVal1 += icVal0;
}


Sriks

 

[Zyrenthian]

Last time i worked with checksums was about a year ago but the way mine worked was the current value and the checksum added together would equal zero. I did something along the lines of this:

return (current_value + (~checksum+1)) == 0;

I dont remember if this was exactly what i did but i do know i used two's compliment to determine if the checksum was correct.


Matt

 

[youssef]

Thanks for your answer

It is work

 

[Zyrenthian]

Great =) glad I could help

Matt