36 lines
1.2 KiB
Cython
36 lines
1.2 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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from ._typedefs cimport 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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# It corresponds to the maximum representable value for
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# 32-bit signed integers (i.e. 2^31 - 1).
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RAND_R_MAX = 2147483647
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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):
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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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# Use the modulo to make sure that we don't return a values greater than the
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# maximum representable value for signed 32bit integers (i.e. 2^31 - 1).
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# Note that the parenthesis are needed to avoid overflow: here
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# RAND_R_MAX is cast to uint32_t before 1 is added.
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return seed[0] % ((<uint32_t>RAND_R_MAX) + 1)
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