libcalcpi_juliac

Description

This repository libcalcpi_juliac provides an example of how to use juliac that offers a more traditional, gcc-like command-line interface for compiling Julia programs. See JuliaHub's blog post New Ways to Compile Julia for more information about juliac.

This repository tries to compile the following Julia function named jlcalcpi which returns the approximate number of π = 3.1415926535897....

function jlcalcpi(N)
    cnt = 0
    for a = 1:N, b = 1:N
        cnt += ifelse(gcd(a, b) == 1, 1, 0)
    end
    prob = cnt / N / N
    return √(6 / prob)
end

Base.@ccallable function calcpi(N::Cint)::Cdouble
    jlcalcpi(N)
end

TL;DR

make && ./a.out

Usage

Install Julia

Install Julia using juliaup

$ curl -fsSL https://install.julialang.org | sh -- --yes

Download juliac

Run make setup to add nightly channel, download juliac.jl and juliac-buildscript.jl

$ ls
Makefile     README.md    libcalcpi.jl main.c
$ make setup

Then we have:

$ ls
Makefile              juliac-buildscript.jl libcalcpi.jl
README.md             juliac.jl             main.c

Build shared library and executable

$ make
Building... shared library
julia +nightly juliac.jl --output-lib libcalcpi.dylib --compile-ccallable --trim libcalcpi.jl
ld: warning: ignoring duplicate libraries: '-ljulia'
ld: warning: reexported library with install name '@rpath/libunwind.1.dylib' found at '/Users/terasakisatoshi/.julia/juliaup/julia-nightly/lib/julia/libunwind.1.0.dylib' couldn't be matched with any parent library and will be linked directly
Done
Building entrypoint
gcc -L./ -lcalcpi main.c -o a.out

We can use the calcpi function from C. This function corresponds to the following implementation in libcalcpi.jl:

Base.@ccallable function calcpi(N::Cint)::Cdouble
    jlcalcpi(N)
end

Run ./a.out

$ ./a.out 10
3.0860669992418384
$ ./a.out 100
3.1395974980055170
$ ./a.out 1000
3.1404153403809061
$ ./a.out 10000 # default value
3.1415342390166292
$ ./a.out
3.1415342390166292

Acknowledgment

This comment by @jbytecode in the Julia Discourse thread 'Where is Juliac developed?' was very helpful.