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