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Full Discussion: Bash - array loop performance
Top Forums Shell Programming and Scripting Bash - array loop performance Post 302919494 by math4 on Wednesday 1st of October 2014 03:24:39 PM
Old 10-01-2014
Bash - array loop performance
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
 

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LEARN ABOUT CENTOS

locale::codes::langext

Locale::Codes::LangExt(3)				User Contributed Perl Documentation				 Locale::Codes::LangExt(3)

NAME

       Locale::Codes::LangExt - standard codes for language extension identification

SYNOPSIS

	  use Locale::Codes::LangExt;

	  $lext = code2langext('acm');		       # $lext gets 'Mesopotamian Arabic'
	  $code = langext2code('Mesopotamian Arabic'); # $code gets 'acm'

	  @codes   = all_langext_codes();
	  @names   = all_langext_names();

DESCRIPTION

       The "Locale::Codes::LangExt" module provides access to standard codes used for identifying language extensions, such as those as defined in
       the IANA language registry.

       Most of the routines take an optional additional argument which specifies the code set to use. If not specified, the default IANA language
       registry codes will be used.

SUPPORTED CODE SETS

       There are several different code sets you can use for identifying language extensions. A code set may be specified using either a name, or
       a constant that is automatically exported by this module.

       For example, the two are equivalent:

	  $lext = code2langext('acm','alpha');
	  $lext = code2langext('acm',LOCALE_LANGEXT_ALPHA);

       The codesets currently supported are:

       alpha
	   This is the set of three-letter (lowercase) codes from the IANA language registry, such as 'acm' for Mesopotamian Arabic.

	   This is the default code set.

ROUTINES

       code2langext ( CODE [,CODESET] )
       langext2code ( NAME [,CODESET] )
       langext_code2code ( CODE ,CODESET ,CODESET2 )
       all_langext_codes ( [CODESET] )
       all_langext_names ( [CODESET] )
       Locale::Codes::LangExt::rename_langext  ( CODE ,NEW_NAME [,CODESET] )
       Locale::Codes::LangExt::add_langext  ( CODE ,NAME [,CODESET] )
       Locale::Codes::LangExt::delete_langext  ( CODE [,CODESET] )
       Locale::Codes::LangExt::add_langext_alias  ( NAME ,NEW_NAME )
       Locale::Codes::LangExt::delete_langext_alias  ( NAME )
       Locale::Codes::LangExt::rename_langext_code  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangExt::add_langext_code_alias  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangExt::delete_langext_code_alias  ( CODE [,CODESET] )
	   These routines are all documented in the Locale::Codes::API man page.

SEE ALSO

       Locale::Codes
	   The Locale-Codes distribution.

       Locale::Codes::API
	   The list of functions supported by this module.

       http://www.iana.org/assignments/language-subtag-registry
	   The IANA language subtag registry.

AUTHOR

       See Locale::Codes for full author history.

       Currently maintained by Sullivan Beck (sbeck@cpan.org).

COPYRIGHT

	  Copyright (c) 2011-2013 Sullivan Beck

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.16.3							    2013-02-27						 Locale::Codes::LangExt(3)
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