Class: Okmain::Xoshiro256PlusPlus

Inherits:
Object
  • Object
show all
Defined in:
lib/okmain/xoshiro.rb

Overview

Xoshiro256++ PRNG, matching Rust’s rand_xoshiro crate exactly. Seeding via SplitMix64 matches Rust’s SeedableRng::seed_from_u64.

Constant Summary collapse

MASK64 = 
(1 << 64) - 1

Instance Method Summary collapse

Constructor Details

#initialize(seed) ⇒ Xoshiro256PlusPlus

Returns a new instance of Xoshiro256PlusPlus.



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# File 'lib/okmain/xoshiro.rb', line 9

def initialize(seed)
  # SplitMix64 seeding (matches Rust's SeedableRng::seed_from_u64)
  sm = seed & MASK64
  @s = Array.new(4) do
    sm = (sm + 0x9e3779b97f4a7c15) & MASK64
    z = sm
    z = ((z ^ (z >> 30)) * 0xbf58476d1ce4e5b9) & MASK64
    z = ((z ^ (z >> 27)) * 0x94d049bb133111eb) & MASK64
    z ^ (z >> 31)
  end
end

Instance Method Details

#next_u64 ⇒ Object

Generate next u64



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# File 'lib/okmain/xoshiro.rb', line 22

def next_u64
  s = @s
  result = (rotl(s[0] + s[3], 23) + s[0]) & MASK64
  t = (s[1] << 17) & MASK64
  s[2] ^= s[0]
  s[3] ^= s[1]
  s[1] ^= s[2]
  s[0] ^= s[3]
  s[2] ^= t
  s[3] = rotl(s[3], 45)
  result
end

#random_f32 ⇒ Object

Uniform f32 in [0, 1), matching Rust’s rand StandardUniform for f32. Xoshiro256++.next_u32() returns next_u64() >> 32 (upper bits). Then StandardUniform takes top 24 bits of the u32.



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# File 'lib/okmain/xoshiro.rb', line 54

def random_f32
  u64 = next_u64
  u32 = u64 >> 32        # Rust's next_u32() for Xoshiro256++
  (u32 >> 8).to_f / 16777216.0 # top 24 bits / 2^24
end

#random_range(range) ⇒ Object

Uniform integer in 0…range, using Lemire’s method (matching Rust’s rand crate)



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# File 'lib/okmain/xoshiro.rb', line 36

def random_range(range)
  full = next_u64 * range
  hi = full >> 64
  lo = full & MASK64
  if lo < range
    threshold = (MASK64 - range + 1) % range # (2^64 - range) % range
    while lo < threshold
      full = next_u64 * range
      hi = full >> 64
      lo = full & MASK64
    end
  end
  hi
end