From: Phrogz <phrogz@...>
Date: 2007-10-26T01:35:03+09:00
Subject: Re: read write integer in binary into a file

On Oct 25, 10:09 am, Adam Preble <pre...@gmail.com> wrote:
> I wrote a function to do this which seems slightly faster, but could
> perhaps stand some optimization:
>
> def pack_int32(n)
>   str = '    '
>   str[3] = n >> 24
>   str[2] = n >> 16
>   str[1] = n >> 8
>   str[0] = n
>   str
> end
>
> Here are the benchmark results vs the other methods mentioned:
>
>                   user     system      total        real
> [].pack(i):   6.234000   0.235000   6.469000 (  6.500000)
> pack_int32:   5.719000   0.015000   5.734000 (  5.734000)
> Marshal.dump: 6.594000   0.219000   6.813000 (  6.813000)
>
> I included Marshal.dump for completeness, but agree that it doesn't
> appear to be meant for this sort of thing.  Here's the source to run
> the benchmark:
>
> require 'benchmark'
> number = 2_000_000
> n = 1_000_000
> Benchmark.bm(12) do |x|
>   x.report('[].pack(i):') { n.times do; [number].pack('i'); end }
>   x.report('pack_int32:') { n.times do; pack_int32(number); end }
>   x.report('Marshal.dump:') { n.times do; Marshal.dump(number); end }
> end

Using only the number 2_000_000 seems to skew the results. I see your
results with your test, but if I change it slightly to use a variety
of integers, I get more balanced results:

  require 'benchmark'
  MAX = 2**30
  n = 1_000_000
  nums = (0..n).map{ (rand*MAX).to_i }

  Benchmark.bmbm do |x|
    x.report('pack(i):') { nums.each{ |num| [num].pack('i') } }
    x.report('pack32:') { nums.each{ |num| pack_int32(num) } }
    x.report('Dump:') { nums.each{ |num| Marshal.dump(num) } }
  end

Rehearsal --------------------------------------------
pack(i):   5.813000   0.109000   5.922000 (  5.984000)
pack32:    5.234000   0.000000   5.234000 (  5.281000)
Dump:      5.906000   0.125000   6.031000 (  6.063000)
---------------------------------- total: 17.187000sec

               user     system      total        real
pack(i):   5.687000   0.125000   5.812000 (  5.875000)
pack32:    5.141000   0.016000   5.157000 (  5.188000)
Dump:      6.000000   0.078000   6.078000 (  6.141000)