A comparison of Reddit's previous and new algorithm

_hot.txt

                                 old            new
# score > 0
_hot(1, 0, 1262304000)           2850.0         2850.0
_hot(1, 0, 1353107345)           4868.0         4868.0
_hot(1000, 500, 1262304000)      2852.69897     2852.69897
_hot(1000, 500, 1353107345)      4870.69897     4870.69897

# score < 0
_hot(0, 1, 1262304000)          -2851.0         2850.0
_hot(0, 1, 1353107345)          -4869.0         4868.0
_hot(1000, 1500, 1262304000)    -2848.30103     2847.30103
_hot(1000, 1500, 1353107345)    -4866.30103     4865.30103

# score == 0
_hot(500, 500, 1353107345)       0.0            4868.0
_hot(1000, 1000, 1262304000)     0.0            2850.0

sorts.rb

require 'date'

def score(ups, downs)
  ups - downs
end

def common_hot(ups, downs, date)
  s = score(ups, downs)
  order = Math.log([s.abs, 1].max, 10)

  sign = if s > 0
    1
  elsif s < 0
    -1
  else
    0
  end

  seconds = date - 1134028003

  return sign, order, seconds
end

def old_hot(ups, downs, date)
  sign, order, seconds = common_hot(ups, downs, date)

  (order + sign * seconds / 45_000).round(7)
end

def new_hot(ups, downs, date)
  sign, order, seconds = common_hot(ups, downs, date)

  (sign * order + seconds / 45_000).round(7)
end

def both_hot(ups, downs, date)
  o = old_hot(ups, downs, date)
  n = new_hot(ups, downs, date)

  { old: o, new: n }
end