nan_bench.pyx

%%cython

cimport numpy as cnp
import numpy as np
cimport cython

cdef extern from "numpy/npy_math.h":
    bint npy_isnan(double x) nogil

cdef inline bint isnan(double x) nogil:
    return x != x

@cython.boundscheck(False)
@cython.wraparound(False)
def isnan_crt(double[:] arr):
    cdef:
        Py_ssize_t i, N=arr.shape[0]
        cnp.uint8_t[:] out = np.empty(N, dtype='uint8')
    with nogil:
        for i in range(N):
            out[i] = npy_isnan(arr[i])
    return np.asarray(out, dtype='bool')

@cython.boundscheck(False)
@cython.wraparound(False)
def isnan_inline(double[:] arr):
    cdef:
        Py_ssize_t i, N=arr.shape[0]
        cnp.uint8_t[:] out = np.empty(N, dtype='uint8')
    with nogil:
        for i in range(N):
            out[i] = isnan(arr[i])
    return np.asarray(out, dtype='bool')
  
a = np.random.randn(int(1e7))
a[::1000] = np.nan