microseconds_benchmark.rb

require 'benchmark'

ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(\.\d+)?\z/
FAST_ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(?:\.(\d+))?\z/
COUNT = 1000000
SRAND = 1455677931
DATETIME_STRING = "2010-01-12 12:34:56.%6.6i"

Benchmark.bm do |bench|
  f = bench.report("Fast") do
    srand(SRAND)
    COUNT.times do
      i0 = rand(1000000)
      str = sprintf(DATETIME_STRING, i0)
      usec = FAST_ISO_DATETIME.match(str)[7].to_i
#      raise unless usec == i0
    end
  end
  s = bench.report("Slow") do
    srand(SRAND)
    COUNT.times do
      i0 = rand(1000000)
      str = sprintf(DATETIME_STRING, i0)
      usec = (ISO_DATETIME.match(str)[7].to_f * 1_000_000).to_i
#      usec = (ISO_DATETIME.match(str)[7].to_f * 1_000_000).round
#      raise unless usec == i0
    end
  end
  delta = ((s.total - f.total) / s.total) * 100.0 
  print "Performance increase: #{delta}\n"
end