#!/bin/bash
# 
# Modified version of bash mandelbrot from Mecki  stackoverflow.com/users/15809
# found at https://stackoverflow.com/a/63749612/1765658
# Avoiding forks and running bc as background task, reducing
# execution time, from many hours to less than 10' (on my desktop)
#
# Modified version tested under MacOS, with bash 3.2.57(1)-release

BAILOUT=16
MAX_ITERATIONS=1000
ALPHWIDTH=$(( `tput cols` / 2 ))
AWIDE=$(( ALPHWIDTH -1 ))

fifo=/tmp/fifo-$RANDOM$RANDOM-$$
mkfifo $fifo
exec 10> >(exec bc -l >$fifo)
exec 11<$fifo
rm $fifo
bc() {
    local retvar="$1"
    shift
    echo >&10 "$@"
    read -ru 11 -t 1 "$retvar"
}
echo >&10 "scale=16;bailout=$BAILOUT;alphwidth=$ALPHWIDTH.0;"

function iterate {
    # $1 is x
    # $2 is y
    local zi=0
    local zr=0
    local i=0

    local cr
    bc cr "$2 - 0.5"
    
    while true
    do
        local temp
        local zr2
        local zi2
        i=$((i + 1))
        bc zr2 "($zr * $zr) - ($zi * $zi) + $cr"
        bc zi2 "(($zr * $zi) * 2) + $1"
        bc temp "(($zi * $zi) + ($zr * $zr)) > bailout"

        if ((temp == 1))
        then
            return "$i"
        fi

        if ((i > MAX_ITERATIONS))
        then
            return 0
        fi

        zr="$zr2"
        zi="$zi2"
    done
}

function mandelbrot {
    local y
    for (( y = 0-AWIDE ; y < AWIDE ; y++ ))
    do
        printf "\n"
        local x
        for (( x = 0 - AWIDE ; x < AWIDE; x++))
        do
            local xi
            local yi
            local ires
            bc xi "$x / alphwidth"
            bc yi "$y / alphwidth"
            iterate "$xi" "$yi"
            ires=$?

            if ((ires == 0))
            then
                printf "*"
            else
                printf " "
            fi
        done
    done
    printf "\n"
}

mandelbrot