Day 15

* $ time ruby 15a.rb
  MRI: 16s
  GraalVM --native: 7s
  With Integer#times written in Ruby to enable OSR: 2s

2017/15a.rb

@@ -0,0 +1,22 @@
+starts = [591, 393]
+factors = [16807, 48271]
+
+Generator = Struct.new(:start, :factor) do
+  def initialize(*)
+    super
+    @n = start
+  end
+
+  def next
+    @n = (@n * factor) % 2147483647
+  end
+end
+
+generators = starts.zip(factors).map { |start, factor|
+  Generator.new(start, factor)
+}
+
+p 40_000_000.times.count {
+  a, b = generators.map { |gen| gen.next % 2**16 }
+  a == b
+}

2017/15b.rb

@@ -0,0 +1,26 @@
+starts = [591, 393]
+factors = [16807, 48271]
+multiples = [4, 8]
+
+Generator = Struct.new(:start, :factor, :multiple) do
+  def initialize(*)
+    super
+    @n = start
+  end
+
+  def next
+    begin
+      @n = (@n * factor) % 2147483647
+    end until @n % multiple == 0
+    @n
+  end
+end
+
+generators = starts.zip(factors, multiples).map { |start, factor, multiple|
+  Generator.new(start, factor, multiple)
+}
+
+p 5_000_000.times.count {
+  a, b = generators.map { |gen| gen.next % 2**16 }
+  a == b
+}