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Bash - array loop performance

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# 8  
Old 10-01-2014
Interesting...that is a major performance difference. I was actually hoping it was cygwin...cause that is dog slow and obvious. I would hope that changes like that to any linux would perform better. I wonder if it is the looping or the frequent math operations done in the assignment. What did you use to profile performance if anything?
This User Gave Thanks to blackrageous For This Post:
math4
# 9  
Old 10-01-2014
Firstly there are already a lot of utilities the encrypt and decrypt files in unix I'd sugget using one of these if you can.

If you must roll you own for all means develop a prototype in shell script, but once it's working I'd suggest converting to C for the final performance version.
# 10  
Old 10-01-2014
Quote:
Originally Posted by Chubler_XL
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

Yes, I read somewhere tha define variable as array speedup the process but when I create the array I use:
Code:
IFS=' ' read   -a  sn <<< "$s"

...so I think was the same. I'm in error?
# 11  
Old 10-01-2014
I used time, and yes associative arrays look to be around 11x faster than normal arrays 5secs vrs 55secs.
# 12  
Old 10-01-2014
<What did you use to profile performance if anything?>

Nothing special.. I had used "LSHW" for the specs and "ps aux" for see cpu usage, and "free" to see ram. Probably I not understand your request.
# 13  
Old 10-01-2014
Quote:
Originally Posted by math4
Yes, I read somewhere tha define variable as array speedup the process but when I create the array I use:
Code:
IFS=' ' read   -a  sn <<< "$s"

...so I think was the same. I'm in error?
If you have a string $s and you want to load the ascii value into an array 1 char at a time you could do this:

Code:
declare -A sn
s="This is a test string"
for((i=0;i<${#s};i++))
do
  printf -v sn[$i] '%d' "'${s:i:1}"
done

echo sn[0]=${sn[0]}
echo sn[1]=${sn[1]}
echo sn[2]=${sn[2]}

Code:
sn[0]=84
sn[1]=104
sn[2]=105

---------- Post updated at 07:37 AM ---------- Previous update was at 07:34 AM ----------

BTW the code I posted before was inaccurate as expressions with [ and ] of an array are not evaluated you need something like this:

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

Which is still faster than without using associative arrays.
This User Gave Thanks to Chubler_XL For This Post:
math4
# 14  
Old 10-01-2014
Quote:
Originally Posted by Chubler_XL
If you have a string $s and you want to load the ascii value into an array 1 char at a time you could do this:
Elements are group of integer, not single char.
I had study "associative arrays" and make a try: It's better, but not so much.
Tomorrow I'll try a vb6 to Perl or Awk conversion. Hope that make difference.

Thank you in any case at all!
Smilie
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