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Full Discussion: String manipulation for sheer speed...
Top Forums UNIX for Dummies Questions & Answers String manipulation for sheer speed... Post 302813239 by agama on Sunday 26th of May 2013 10:16:10 PM
Old 05-26-2013
Have you tried reading the data into an array which would allow you to avoid the substring overhead which I believe is costing you. Your original code ran in about 4 seconds for me using Bash and less than a second with Kshell. The code below, which reads and processes the array, runs much faster under both:

Kshell .07s
Bash .17s

Maybe I'm missing something but this seems to perform pretty well.

Code:
# "decimalstring" is an array of the first 8192 bytes from the input file
# (the variable name is now misleading, but I left it the same as in the original code)
decimalstring=(  $( hexdump -n8192 -s0 -v -e '1/1 "%u "' input-file )  )

n=0
m=0

printf "\nStart!"

# Start position of slow loop.
for (( i = 0; i < 8192; i++ ))
do
        if (( ${decimalstring[$i]} >= 127 ))
        then
                ((m++))
        else
                ((n++))
        fi
done
# End position of slow loop.

printf "\n\nDone!, m=$m, n=$n...\n\n"


The raw output:
Code:
spot:[/home/scooter/src/test]time bash tt18

Start!

Done!, m=2063, n=6129...


real    0m0.17s
user    0m0.17s
sys     0m0.01s
spot:[/home/scooter/src/test]time ksh tt18

Start!

Done!, m=2063, n=6129...


real    0m0.07s
user    0m0.06s
sys     0m0.01s

Last edited by agama; 05-26-2013 at 11:22 PM.. Reason: code tag broken
This User Gave Thanks to agama For This Post:
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LEARN ABOUT POSIX

times

TIMES(1P)						     POSIX Programmer's Manual							 TIMES(1P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       times -- write process times

SYNOPSIS

       times

DESCRIPTION

       The times utility shall write the accumulated user and system times for the shell and for all of its  child  processes,	in  the  following
       POSIX locale format:

	   "%dm%fs %dm%fs
%dm%fs %dm%fs
", <shell user minutes>,
	       <shell user seconds>, <shell system minutes>,
	       <shell system seconds>, <children user minutes>,
	       <children user seconds>, <children system minutes>,
	       <children system seconds>

       The  four  pairs  of  times  shall  correspond to the members of the <sys/times.h> tms structure (defined in the Base Definitions volume of
       POSIX.1-2008, Chapter 13, Headers) as returned by times(): tms_utime, tms_stime, tms_cutime, and tms_cstime, respectively.

OPTIONS

       None.

OPERANDS

       None.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       None.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       See the DESCRIPTION.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       Zero.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

       $ times
       0m0.43s 0m1.11s
       8m44.18s 1m43.23s

RATIONALE

       The times special built-in from the Single UNIX Specification is now required for all conforming shells.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Section 2.14, Special Built-In Utilities

       The Base Definitions volume of POSIX.1-2008, <sys_times.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy  --	Portable  Operating  System  Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013								 TIMES(1P)
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