# "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"

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