erfc_libm vs erfc_python

from cffi import FFI
ffi = FFI()
ffi.cdef('double erfc(double x);')
libm = ffi.dlopen("m")
erfc = libm.erfc

from math import erfc as p_erfc
from numba import njit
from numpy import linspace

@njit
def test_loop_libm(x):
    t = 0.0
    for i in range(x.shape[0]):
        e = x[i]
        t += erfc(e)
    return t

@njit
def test_loop_cpython(x):
    t = 0.0
    for i in range(x.shape[0]):
        e = x[i]
        t += p_erfc(e)
    return t

x = linspace(0.5,1.0,100000)

assert( abs(test_loop_cpython(x)  -  test_loop_libm(x))<1e-8 )



import time
t1 = time.time()
for i in range(100):
    test_loop_cpython(x)
t2 = time.time()
for i in range(100):
    test_loop_libm(x)
t3 = time.time()

print('cpython: {}'.format(t2-t1))
print('libm: {}'.format(t3-t2))