From: Adam Preble <preble@...>
Date: 2007-10-26T01:09:13+09:00
Subject: Re: read write integer in binary into a file

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

Adam

On Oct 25, 10:36 am, Vianney Lecroart <ace...@gmail.com> wrote:
> Hello,
>
> I have some big files with lot of "unsigned int" (4 bytes) numbers and I
> want to read and write on these files.
>
> Currently, I found this to write:
>
> myfile << [mynum].pack("i")
>
> and to read:
>
> mynum = myfile.read(4).unpack("i").first
>
> I wonder if there's not something faster/simpler to do that without the
> need to convert the number into an array into a string to finally
> serialize it.
>
> Thank you.