FFI — Foreign Function Interface
Simple header file with defintions:
void sunpos(double d, double *L, double *M, double *ra, double *decl, double *rad);
In PHP, load definitions and call:
<?php
$ffi = FFI::load(__DIR__ . '/astro.h');
$dayNr = (time() - 946598400) / 86400.0;
$L = FFI::new('double');
$M = FFI::new('double');
$ra = FFI::new('double');
$decl = FFI::new('double');
$rad = FFI::new('double');
$ffi->sunpos(
$dayNr,
FFI::addr($L), FFI::addr($M), FFI::addr($ra), FFI::addr($decl), FFI::addr($rad)
);