cffi with numpy example

_output.txt

[2.99616175+5.54885256j 2.50767967+4.65893257j 4.13392399+1.69048949j
 0.93860821+1.46470066j 5.6235234 +2.36071585j 2.28013476+4.78671259j
 3.34736328+4.25295228j 5.7851614 +5.63424175j 1.90595192+2.16040048j
 1.62844748+0.06384722j 0.89949666+4.65337538j 1.95680565+2.67681418j
 5.78686059+5.3124304j  1.9592114 +0.16909678j 2.01095818+3.03112179j
 4.20331404+3.13157214j 0.05917195+2.77188645j 5.47970406+1.40063894j
 2.05722142+2.48133127j 4.59507957+5.93884264j 0.17166239+4.79953363j
 5.44861648+1.22816477j 3.39911951+2.21297174j 0.01094132+0.19348674j
 0.82714832+1.73206116j]
[0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j
 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j
 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j]
[-1.27117005e+02-1.86176212e+01j -4.25147579e+01-3.12480509e+01j
 -1.53266429e+00+2.19277272e+00j  1.34650840e+00-1.65183359e+00j
  4.22475741e+00+3.21874284e+00j -3.90521940e+01-4.54889535e+01j
 -3.44216410e+01+7.18174722e+00j  1.22928158e+02+6.68391763e+01j
 -1.44556821e+00-4.04154175e+00j -5.77367066e-02-6.37844654e-02j
  3.26390856e+01-4.10804605e+01j -2.74981776e+00-6.70260361e+00j
  8.91858454e+01+4.82953437e+01j -3.84149474e-01-1.57247733e-01j
 -4.42463038e+00-9.35089196e+00j -5.59344896e+00+9.98338633e+00j
  8.01160963e+00-4.70917936e-01j  1.49400986e+00+1.37166217e+00j
 -2.81434904e+00-5.24816217e+00j -2.22083313e+01+1.88442314e+02j
  5.98383833e+01-1.03726954e+01j  1.24488406e+00+1.15675908e+00j
 -4.47355460e+00+1.15036621e+00j  1.01871605e+00-2.13019111e-03j
  1.97312214e+00-2.01494772e+00j]
[-1.27117005e+02-1.86176212e+01j -4.25147579e+01-3.12480509e+01j
 -1.53266429e+00+2.19277272e+00j  1.34650840e+00-1.65183359e+00j
  4.22475741e+00+3.21874284e+00j -3.90521940e+01-4.54889535e+01j
 -3.44216410e+01+7.18174722e+00j  1.22928158e+02+6.68391763e+01j
 -1.44556821e+00-4.04154175e+00j -5.77367066e-02-6.37844654e-02j
  3.26390856e+01-4.10804605e+01j -2.74981776e+00-6.70260361e+00j
  8.91858454e+01+4.82953437e+01j -3.84149474e-01-1.57247733e-01j
 -4.42463038e+00-9.35089196e+00j -5.59344896e+00+9.98338633e+00j
  8.01160963e+00-4.70917936e-01j  1.49400986e+00+1.37166217e+00j
 -2.81434904e+00-5.24816217e+00j -2.22083313e+01+1.88442314e+02j
  5.98383833e+01-1.03726954e+01j  1.24488406e+00+1.15675908e+00j
 -4.47355460e+00+1.15036621e+00j  1.01871605e+00-2.13019111e-03j
  1.97312214e+00-2.01494772e+00j]

builder.py

from cffi import FFI
ffibuilder = FFI()

ffibuilder.set_source("_example", """

#include <complex.h>

void
mangle(size_t n, double complex* a_in, double complex* a_out)
{
    for (size_t i = 0; i < n; ++i) {
        a_out[i] = ccos(a_in[i]);
    }
}

""", libraries=[])

ffibuilder.cdef("""
// pycparser supports the C99 _Complex but not the 'complex' shorthand. this
// could also just be void* since it's all using numpy anyway.
void
mangle(size_t n, double _Complex* a_in, double _Complex* a_out);
""")

ffibuilder.compile(verbose=True)

example.py

import math, numpy.random
from _example import ffi, lib
a = (
    numpy.random.uniform(0, math.tau, 25)
    + 1j * numpy.random.uniform(0, math.tau, 25)
).astype(numpy.cdouble)
b = numpy.zeros_like(a)
print(a)
print(b)

def for_cffi(arr):
    return ffi.cast('double _Complex*', ffi.from_buffer(arr))

lib.mangle(len(a), for_cffi(a), for_cffi(b))
print(b)
print(numpy.cos(a))