#1 2017-06-10 22:30:28

brontosaurusrex

Middle Office

Registered: 2015-09-29

Posts: 2,744

bash rounding

This bash function

#!/bin/bash

# awk_round

awk_round () {
    awk 'BEGIN{printf "%3."'$1'"f\n", "'$2'"}'
}

awk_round "$1" "$2"

seems to work as expected and it is faster than using bc (which also behaves unexpectedly).

awkround 0 42.1
42
awkround 0 42.5
42
awkround 0 42.6
43
awkround 0 -42.6
-43

However one can still use bc in scripts, just perhaps send the floating results to this fancy function (if you need rounding).

Last edited by brontosaurusrex (2017-06-10 22:38:06)

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DeepDayze

Like sands through an hourglass...

From: In Linux Land

Registered: 2017-05-28

Posts: 1,897

Re: bash rounding

Nice one...maybe we should have a place where people can contribute some good functions (portably written of course).

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brontosaurusrex

Middle Office

Registered: 2015-09-29

Posts: 2,744

Re: bash rounding

p.s. speedtest example comparing awk with bc with python

#!/bin/bash

# roundtest

#set -x
#a="-3.6"
#n="0"

awk_round () {
    awk 'BEGIN{printf "%3."'$1'"f\n", "'$2'"}'
}

bc_round () {
    echo $(printf %.$2f $(echo "scale=$2;(((10^$2)*$1)+0.5)/(10^$2)" | bc))
}

py_round () {
    echo "print '{0:g}'.format(round($1,$2))" | python
}

# awk = pass
echo "awk"
a=$(awk_round "0" "-3.6")
echo "$a"

time (for ((i=1;i<=100;i++)); 
do 
    awk_round "0" "-3.6" > /dev/null
done)

# bc = fail
echo "bc"
b=$(bc_round "-3.6" "0")
echo "$b"

time (for ((i=1;i<=100;i++)); 
do 
    bc_round "-3.6" "0" > /dev/null
done)

# python = pass
echo "python"
c=$(py_round "-3.6" "0")
echo "$c"

time (for ((i=1;i<=100;i++)); 
do 
    py_round "-3.6" "0" > /dev/null
done)

It would be probably interesting to add python function to this test. Added python func.

Last edited by brontosaurusrex (2017-06-10 23:20:42)

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brontosaurusrex

Middle Office

Registered: 2015-09-29

Posts: 2,744

Re: bash rounding

nobody: Very interesting (over my head), how "portable" is that?

Last edited by brontosaurusrex (2017-06-10 23:29:10)

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damo

....moderator....

Registered: 2015-08-20

Posts: 6,734

Re: bash rounding

Nice one...maybe we should have a place where people can contribute some good functions (portably written of course).

There is - "Scripts, Tutorials and Tips"

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DeepDayze

Like sands through an hourglass...

From: In Linux Land

Registered: 2017-05-28

Posts: 1,897

Re: bash rounding

Nice one...maybe we should have a place where people can contribute some good functions (portably written of course).

There is - "Scripts, Tutorials and Tips"

oh my bad

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brontosaurusrex

Middle Office

Registered: 2015-09-29

Posts: 2,744

Re: bash rounding

Not sure if this is even a correct zsh script, but here: awk vs zsh

#!/usr/bin/zsh
# zsh roundtest

awk_round () {
    awk 'BEGIN{printf "%3."'$1'"f\n", "'$2'"}'
}

zsh_round () {
    printf %.$1f $(($2))
 }
 
# awk = pass
echo "awk"
a=$(awk_round "0" "-3.6")
echo "$a"

time (for ((i=1;i<=100;i++)); 
do 
    awk_round "0" "-3.6" > /dev/null
done)

# zsh = ?
echo "zsh"
z=$(zsh_round "0" "-3.6")
echo "$z"

time (for ((i=1;i<=100;i++)); 
do 
    zsh_round "0" "-3.6" > /dev/null
done)

Actuall perhaps this should be bash script as well (the one that calls zsh).

@nobody: ctypes vs zsh?

Last edited by brontosaurusrex (2017-06-12 11:18:39)

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