Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: linux-gnu
Compiler: gcc
Compilation CFLAGS: -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE=$
uname output: Linux tom-VirtualBox 3.19.0-69-generic #77~14.04.1-Ubuntu SMP Tue Aug 30 01:29:21 UTC 2016 $
Machine Type: x86_64-pc-linux-gnu
Bash Version: 4.3
Patch Level: 11
Release Status: release
Description:
Two nearly identical "For Loop" setups have large deltas in performance. See test program below. Was confirmed in IRC chat room by multiple users. Input is very noticeable with around 100,000 values.
The script was originally used to take an input file where the first line would determine how many int values were to follow. The remaining lines each had values that were sorted, and then the smallest difference between any two values were found.
Repeat-By:
Using script below comment/uncomment each method to test.
On my machine
Method-1 finishes in around 2 seconds
Method-2 finishes in around 72 seconds
---- Code Below (also attached script and test input file) ---
START=$(date +%s.%N)
read -r N && mapfile -t Pi < <(sort -n)
#echo "Done"
min=10000000
#Find the smallest difference between two numbers in sorted array with max array element = 10000000
# For-Loop Method-1: is super fast
for (( i=0; i<N-1; i++ ))
do
current=${Pi[$i]}
next=${Pi[$i+1]}
diff=$(( next - current))
if [ $diff -lt $min ]
then
min=$diff
fi
done
# For-Loop Method-2: is super slow
# for (( i=0; i<N-1; i++)); do
# if (( Pi[i+1] - Pi[i] < min )); then
# let min=Pi[i+1]-Pi[i]
# fi
# done
#The min difference between any two numbers in the array
echo "$min"
END=$(date +%s.%N)
DIFF=$(echo "$END - $START" | bc)
echo "$DIFF"
Thanks,
Tom
--
longinput.txt
brokenForLoop.sh