##result
                user     system      total        real
jj          3.130000   0.130000   3.260000 (  7.560419)
joekarma    2.110000   0.080000   2.190000 (  4.912987)
b_jonas     4.640000   0.190000   4.830000 ( 19.871645)

##code
require 'benchmark'

string = <<EOF
This is the test string.
I'm putting text in here because, well,
I need to fill up a string in order to perform tests
with it.

I wonder whos function will fair the best?

Time will tell!
EOF

def line_at_pos(pos, str)
  pos = str.length + pos if pos < 0
  pos = 0 if pos < 0
  l = (str.rindex(/[\r\n]/, pos) || -1) + 1
  r = (str.index(/[\r\n]/, pos) || str.length) - 1
  str[l..r]
end

def line_at_pos_2(pos, str)
  str.inject(pos) { |pos, line| break line.chomp if line.length >= pos ; pos - line.length }
end

def line_at_pos_3(pos, str)
  (str =~ /\A.{0,#{pos}}^(?-m:.*)/m)[1]
end

$times = 100000
Benchmark.bm(10) do |bm|
  bm.report('jj') do
    $times.times do
      line_at_pos_2(rand(string.length), string)
    end
  end
  bm.report('joekarma') do
    $times.times do
      line_at_pos(rand(string.length), string)
    end
  end
  bm.report('b_jonas') do
    $times.times do
      line_at_pos_3(rand(string.length), string)
    end
  end
end