问Bash取模奇怪的结果(不是负的)

EN

#!/bin/bash

if [ $# -ne 2 ]
then 
        echo "Fout, syntaxis: $0 maand(in cijfers) jaar"
        exit 1
fi

a=$(echo "14 - $1"|bc)
y=$(echo "$2 + 4800 - $a"|bc)
m=$(echo "12 * $a - 3 + $1"|bc)
jdn=$(echo "scale=2;1 + (153 * $m +2)/5 + 365 * $y +${y}/4 - ${y}/100     - 32045"|bc)
jdn=$(echo "$jdn + 1"|bc|sed "s/...$//")
d=1
p=$(echo "29.530588853")

while [ "$d" != "32" ]
do
        echo -n "$d"
        days=$(echo "scale=2;${jdn} % ${p}"|bc) 
    fase=$(echo "scale=2;$p / $days"|bc)
    fase1=$(echo "${fase}<7.382647213"|bc)
    if [ $fase1 -eq 1 ]
    then
            echo -n "@"
    elif [ $(echo "${fase}<14.76529443"|bc) -eq 1 ]
    then
            echo -n ")"
    elif [ $(echo "$fase<22.14794164"|bc) -eq 1 ]
    then
            echo -n "0"
    else
            echo -n "("
    fi
    d=$(echo "$d + 1"|bc)
    jdn=$(echo "$jdn +1"|bc)
done