concurrent_pi_ex

#!/bin/bash
#
# Example that corresponds to "Concurrent pi" on https://go.dev/play/.
# License for the corresponding code https://go.dev/LICENSE?m=text.

readonly DIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
. ${DIR}/../../gobash


function bcs() {
        # Unit function for bc with specific scale.
        local -r exp="${1}"
        shift 1

        bc <<< "scale=4; ${exp}"
}

function pi() {
        local -r n="${1}"
        shift 1

        local -r ch=$(Chan)
        for k in $(seq 0 "${n}"); do
                ( term "$ch" "${k}" ) &
        done

        local f="3.0"
        for k in $(seq 0 "${n}"); do
                local v=$($ch recv)
                f=$(bcs "${f} + ${v}")
        done

        echo "${f}"
}

function term() {
        local -r ch="${1}"
        local -r k="${2}"
        shift 2

        local -r ke=$(bcs "-1^${k}")
        local -r k2=$(bcs "2 * ${k} + 2")
        local -r k3=$(bcs "2 * ${k} + 3")
        local -r k4=$(bcs "2 * ${k} + 4")

        local val=$(bcs "4 * ${ke} / (${k2} * ${k3} * ${k4})")
        $ch send "${val}"
}

function main() {
        printf "MATH_PI %g\n" $MATH_PI
        printf "Nilakantha %g\n" $(pi 10)
}

main