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# Authors: Arnaud Joly
#
# License: BSD 3 clause
import numpy as np
cimport numpy as np
ctypedef np.npy_uint32 UINT32_t
cdef inline UINT32_t DEFAULT_SEED = 1
cdef enum:
# Max value for our rand_r replacement (near the bottom).
# We don't use RAND_MAX because it's different across platforms and
# particularly tiny on Windows/MSVC.
RAND_R_MAX = 0x7FFFFFFF
cpdef sample_without_replacement(np.int_t n_population,
np.int_t n_samples,
method=*,
random_state=*)
# rand_r replacement using a 32bit XorShift generator
# See http://www.jstatsoft.org/v08/i14/paper for details
cdef inline UINT32_t our_rand_r(UINT32_t* seed) nogil:
"""Generate a pseudo-random np.uint32 from a np.uint32 seed"""
# seed shouldn't ever be 0.
if (seed[0] == 0): seed[0] = DEFAULT_SEED
seed[0] ^= <UINT32_t>(seed[0] << 13)
seed[0] ^= <UINT32_t>(seed[0] >> 17)
seed[0] ^= <UINT32_t>(seed[0] << 5)
# Note: we must be careful with the final line cast to np.uint32 so that
# the function behaves consistently across platforms.
#
# The following cast might yield different results on different platforms:
# wrong_cast = <UINT32_t> RAND_R_MAX + 1
#
# We can use:
# good_cast = <UINT32_t>(RAND_R_MAX + 1)
# or:
# cdef np.uint32_t another_good_cast = <UINT32_t>RAND_R_MAX + 1
return seed[0] % <UINT32_t>(RAND_R_MAX + 1)
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