From: Joel VanderWerf <vjoel@...>
Date: 2006-03-22T16:10:48+09:00
Subject: Re: Round floats to N decimal places?

Joel VanderWerf wrote:
> Oh what the heck, here's the benchmark, and the winner is... strings!

Oops. I got the benchmark labels backwards. Strings are slower. Here's
the correct code and output:

require 'benchmark'

n = 1000000
the_float = 1.0/7

raise unless ("%0.2f" % the_float).to_f == (the_float*100).round/100.0

Benchmark.bmbm(10) do |rpt|
  rpt.report("float rounding") do
    n.times {
      (the_float*100).round/100.0
    }
  end

  rpt.report("string rounding") do
    n.times {
      ("%0.2f" % the_float).to_f
    }
  end
end

__END__

Output:

Rehearsal ---------------------------------------------------
float rounding    2.210000   0.000000   2.210000 (  2.884535)
string rounding   3.210000   0.000000   3.210000 (  6.516337)
------------------------------------------ total: 5.420000sec

                      user     system      total        real
float rounding    2.190000   0.000000   2.190000 (  4.398573)
string rounding   3.170000   0.010000   3.180000 (  6.466687)

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407