(1..15).each do |size|
  (-16..16).each do |n|
    m = n
    
    n %= size if n.abs >= size
    n += size if n < 0
    
    m %= size
    
    raise ":(" if n != m
  end
end

require "benchmark"
Benchmark.ips do |x|
  x.report("old") do
    (1..15).each do |size|
      (-15..15).each do |n|
        n %= size if n.abs >= size
        n += size if n < 0
      end
    end
  end
  x.report("new") do
    (1..15).each do |size|
      (-15..15).each do |n|
        n %= size
      end
    end
  end
end