ChudnovskyPi_julia.jl

# Chudnovsky algorithm for Pi
# https://en.wikipedia.org/wiki/Chudnovsky_algorithm
# Juhani Kaukoranta 14.06.2022
function Chudnovsky(digits)
    # digits : how many decimals of Pi to be calucate
    maxK = trunc(Int,digits*0.071+2) # max numbers of iterations
    prec = round(BigInt,log2(BigFloat(10.0)^(digits+8))) # bit precision
    setprecision(prec) # bit precision,not number precision
    K, M, L, X, S = big(6), big(1), big(13591409), big(1), big(13591409)
    for k = 1 : maxK
        M = div((big(K)^3 - 16*big(K))*M, k^3)
        L += big(545140134)
        X *= big(-262537412640768000)
        S += big(M)*big(L)/big(X)
        K += 12
    end
    pii = big(426880)*sqrt(big(10005)) / big(S)
    pi = string(pii)
    return(pi[1:digits+2])
end