Ruby

Add optimization for creating zerofill string

require 'benchmark'
n = 1 * 1024 * 1024 * 1024
Benchmark.bmbm do |x|
  x.report("*") { 0.chr * n }
  x.report("ljust") { String.new(capacity: n).ljust(n, "\0") }
end

Before

Rehearsal -----------------------------------------
*       0.358396   0.392753   0.751149 (  1.134231)
ljust   0.203277   0.389223   0.592500 (  0.594816)
-------------------------------- total: 1.343649sec

            user     system      total        real
*       0.282647   0.304600   0.587247 (  0.589205)
ljust   0.201834   0.283801   0.485635 (  0.487617)

After

Rehearsal -----------------------------------------
*       0.000522   0.000021   0.000543 (  0.000534)
ljust   0.208551   0.321030   0.529581 (  0.542083)
-------------------------------- total: 0.530124sec

            user     system      total        real
*       0.000069   0.000006   0.000075 (  0.000069)
ljust   0.206698   0.301032   0.507730 (  0.517674)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59614 b2dd03c8-39d4-4d8f-98ff-823fe69b080e