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require 'concurrent/thread_safe/util'
module Concurrent
# @!visibility private
module ThreadSafe
# @!visibility private
module Util
# A xorshift random number (positive +Fixnum+s) generator, provides
# reasonably cheap way to generate thread local random numbers without
# contending for the global +Kernel.rand+.
#
# Usage:
# x = XorShiftRandom.get # uses Kernel.rand to generate an initial seed
# while true
# if (x = XorShiftRandom.xorshift).odd? # thread-localy generate a next random number
# do_something_at_random
# end
# end
module XorShiftRandom
extend self
MAX_XOR_SHIFTABLE_INT = MAX_INT - 1
# Generates an initial non-zero positive +Fixnum+ via +Kernel.rand+.
def get
Kernel.rand(MAX_XOR_SHIFTABLE_INT) + 1 # 0 can't be xorshifted
end
# xorshift based on: http://www.jstatsoft.org/v08/i14/paper
if 0.size == 4
# using the "yˆ=y>>a; yˆ=y<<b; yˆ=y>>c;" transform with the (a,b,c) tuple with values (3,1,14) to minimise Bignum overflows
def xorshift(x)
x ^= x >> 3
x ^= (x << 1) & MAX_INT # cut-off Bignum overflow
x ^= x >> 14
end
else
# using the "yˆ=y>>a; yˆ=y<<b; yˆ=y>>c;" transform with the (a,b,c) tuple with values (1,1,54) to minimise Bignum overflows
def xorshift(x)
x ^= x >> 1
x ^= (x << 1) & MAX_INT # cut-off Bignum overflow
x ^= x >> 54
end
end
end
end
end
end
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