Test and fix for Sonic Pi's spread function

spread2.rb

def redistribute(v1, v2)
  vNew = []
  while v1.length > 0 && v2.length > 0
    a1 = v1.shift
    a2 = v2.shift
    vNew.unshift(a1 + a2)
  end
  if v1.length > 0 then
    [vNew, v1]
  else
    [vNew, v2] # might be empty, but that's fine
  end
end

# no error checks, e.g. negative, num_accents > size
# no rotation
def spread2(num_accents, size)
  v1 = [[true]] * num_accents
  # If v2 empty -> end
  if num_accents == size
    v1
  else
    v2 = [[false]] * (size - num_accents)
    # If v2 not empty, call at least once.
    (v1, v2) = redistribute(v1,v2)
    # End condition: v2 empty or has just one element.
    while v2.length > 1
      (v1, v2) = redistribute(v1,v2)
    end
    (v1 + v2).flatten
  end
end


# "pretty" print a rythm
def ppeu(r)
  result = ""
  r.length.times do |i|
    if r[i] then
      result = result + "x"
    else
      result = result + "."
    end
  end
  result
end

def test(a, b, r, rot = 0)
  # result = ppeu(spread(a, b, rotate: rot))
  result = ppeu(spread2(a, b)) # ignores rotation
  if result == r then
    #    puts "ok: " + a.to_s + b.to_s
  else
    puts "nok: " + a.to_s + " " + b.to_s + " gives " + result + " but should " + r
  end
end

# I don't yet understand why the computation
# res << ((i * num_accents % size) < num_accents)
# gives the same rhythm as the algorithm by Toussaint
# but all tested are in the same necklace at least

# chapter 2
test(5, 13,"x..x.x..x.x..", 1)

# chapter 4
test(1, 2, "x.")
test(1, 3, "x..")
test(1, 4, "x...")
test(4, 12, "x..x..x..x..")
test(2, 3, "x.x")
test(2, 5, "x.x..", 1)
test(3, 4, "x.xx")
test(3, 5, "x.x.x")
test(3, 7, "x.x.x..", 1)
test(3, 8, "x..x..x.")
test(4, 7, "x.x.x.x")
test(4, 9, "x.x.x.x..", 1)
test(4, 11, "x..x..x..x.")
test(5, 6, "x.xxxx")
test(5, 7, "x.xx.xx")
test(5, 8, "x.xx.xx.", 1)
test(5, 9, "x.x.x.x.x")
test(5, 11, "x.x.x.x.x..", 1)
test(5, 12, "x..x.x..x.x.")
test(5, 16, "x..x..x..x..x...", 1) # obvious misprint in the paper
test(7, 8, "x.xxxxxx")
test(7, 12, "x.xx.x.xx.x.", 2)
test(7, 16, "x..x.x.x..x.x.x.")
test(9, 16, "x.xx.x.x.xx.x.x.", 3)
test(11, 24, "x..x.x.x.x.x..x.x.x.x.x.")
test(13, 24, "x.xx.x.x.x.x.xx.x.x.x.x.", 5)