Shell Programming and Scripting

Hi,

another little question...

"sn" is an array whose elements can vary from about 55,000 to about 150,000 elements. Each element consists of an integer between 0-255, eg: ${sn[1]} contain the value: 103 . For a decrypt-procedure I need scroll all the elements 4 or 5 times. Here is an example of one of the loop where n is length of sn array:

Code:

 for(( i=0; i<n-2; i++ ))
 do sn[$i]=$((${sn[$i]} ^ ${sn[$i+2]} ^ (${sn[$i+1]} * k4) % 256))
 done

 for(( i=(n-1); i>1; i--))
 do sn[$i]=$(( ${sn[$i]} ^ ${sn[$i-2]} ^ (${sn[$i-1]} * k3) % 256))
 done

It all works ... but it takes 3 minutes to loop even when the equivalent vb6 takes me globally no more than 10 seconds.

Code:

For i = 1 To n - 2: sn(i) = sn(i) Xor sn(i + 2) Xor (k4 * sn(i + 1)) Mod 256: Next

I'm doing something wrong? The script is successful without any errors.
I had tried some things... for example work in "do" section with small array in this way:

Code:

a=${sn[@]:i:3};
IFS=' ' read -a an <<< "$a"
x=$an{[0]};
y=$an{[1]};
z=$an{[2]};
sn[i]=$(( x ^ z ^ (y*4) % 256 ))

but seems doesn't change much. Any idea how can I increase my loop performance?

thank you
math

maybe it's not the language construct so much as it's the hardware. Do you mean Visual Basic. What are the physical machines?

I don't think bash is too good at maths, even though you are dealing with integer math only...

Hi, thank you for reply.
It's the same machine (P4) that had XP sp3 (32bit), and now run with only ubunto server (without X... and I don't want install WINE).

product: Intel(R) Pentium(R) 4 CPU 2.66GHz
vendor: Intel Corp.
size: 2700MHz
width: 32 bits
ram: 1.5gb


The vb6 prog was a simple .bas service and was very fast.
The bash conversion that I made is very fast everywhere but in loops menthioned is damn slow. Same machine.

---------- Post updated at 03:08 PM ---------- Previous update was at 02:50 PM ----------

Mmm I'm newbie in Linux, do you suggest rewrite the entire script in some else?

What could I use that is already installed in ubuntu-server? ..and preferably that allows me to import a little 'bash code already written?

NOTE: I had try now to remove all math expression/logic code inside each (5) loops present in the script. Execution time it's now about 5 secs!

Use awk or perl its good for maths, please show a representative sample of input, desired output with brief description .

Bash isn't very efficient looking up large arrays I found using bash 4 assoicative arrays gave me a significant boost in speed if you have bash 4 consider using them:

Code:

declare -A sn
n=80000
k4=2
k3=6
for((i=0;i<n;i++))
do  sn[i]=$((RANDOM%256))
done

for(( i=0; i<n-2; i++ ))
do sn[i]=$(( (sn[i] ^ sn[i+1] ^ sn[i+2] * k4) % 256 ))
done

for(( i=(n-1); i>1; i--))
do sn[i]=$(( (sn[i] ^ sn[i-2] ^ sn[i-1] * k3) % 256))
done

Brief:
I read a binary file encrypted, parse char by char loaded using a key, and then, with the result, I create a new file readable.