#!/bin/bash
if ! [[ "$1" =~ ^[0-9]+$ ]]; then
    echo "Usage: randint <positive integer> [fast]"
    exit 1
fi
number=$1
ceiling=$(echo "l($number +1)/l(2)" | bc -l | awk '{
    bits = ($1 == int($1)) ? $1 : int($1) + 1;
    print int( (bits + 7) / 8 )
}')

if [[ "$2" == "fast" ]]; then
    random_num=$(xxd -p -l $ceiling /dev/urandom | tr -d '\n' | awk -v num="$number+1" '{print strtonum("0x" $0) % num}')
else
    while :; do
        random_num=$(xxd -p -l $ceiling /dev/urandom | tr -d '\n' | awk '{print strtonum("0x" $0)}')
        (( random_num < number )) && break
    done
fi
echo $random_num