in_circle.pyx

%%cython
#cython: boundscheck=False, wraparound=False
import numpy as np
cimport numpy as np
from cpython cimport array
    
def sum_array(array.array arr):
    cdef int i
    cdef double s = 0
    for i in range(len(arr)):
        s += arr.data.as_doubles[i]
    return s

def where_1d(x):
    cdef array.array[int] pos = array.array("i")
    cdef int i
    cdef unsigned char[::1] xview = x.view("uint8")
    for i in range(xview.shape[0]):
        if xview[i]:
            pos.append(i)
            #array.extend_buffer(pos, <char*>(&i), 1)
    return pos

def in_circle(double[:, :] points, double cx, double cy, double r):
    cdef array.array[double] res = array.array("d")
    cdef double r2 = r * r
    cdef double p[2]
    cdef int i
    for i in range(points.shape[0]):
        p[0] = points[i, 0]
        p[1] = points[i, 1]
        if (p[0] - cx)**2 + (p[1] - cy)**2 < r2:
            array.extend_buffer(res, <char*>p, 2)
    return np.frombuffer(res, np.double).copy().reshape(-1, 2)