#!/bin/bash
# vi:set ts=8 sw=4 et sta:
#
# Author : Clark J. Wang <dearvoid at gmail.com>
# License: GPLv2
# 
# $Date$
# $Author$
# $HeadURL$
# $Revision$
#
#--------------------------------------------------------------------#

is_prime()
{
    local n=$1

    # not a valid integer, return false
    [ "${n//[0-9]/}" ] && return 1

    # 0, 1 are not prime
    ((n < 2)) && return 1

    if ((n & 1)); then
        # odd
        local n_2=$((n >> 1))
        local i
        for ((i = 3; i < n_2; i += 2)); do
            ((n % i)) || return 1
        done

        return 0
    else
        # even, only 2 is prime
        ((n > 2)) && return 1 || return 0
    fi
}

#-- main() ----------------------------------------------------------#

{
    declare -i N=$1
    [ $N -le 0 ] && N=200
    echo "Prime numbers in [1, $N) :"
    echo "------------------------------"
    count=0
    for ((n = 0; n < N; ++n)); do
        if is_prime $n; then
            printf "%8d" $n
            ((++count % 8)) || echo
        fi
    done
    ((count % 8)) && echo
    echo "------------------------------"
    echo "Total: $count"
}