From: Masahiro Tanaka <masa@...>
Date: 2000-12-13T06:17:56+09:00
Subject: [ruby-talk:7109] Re: Reading lots of binary data into arrays

>From: matz@zetabits.com (Yukihiro Matsumoto)
>Subject: [ruby-talk:7067] Re: Reading lots of binary data into arrays

> In message "[ruby-talk:7049] Reading lots of binary data into arrays"
>     on 00/12/12, Dwight Tuinstra <tuinstra@clarkson.edu> writes:
> 
> |1)  Are there packages/extensions/modules available
> |    for reading large amounts of binary data into arrays
> |    of structures?  I know that binary data can be read
> |    a "char" at a time, but this is likely to be too
> |    slow.
> 
> Read fixed sized string using IO#read then unpack it into integers
> using String#unpack.  For example:

>   while str = input.read(size_of_an_entry)
>     ary.push(str.unpack("NNNnn")) # assuming network byte order
>   end

If you need more speed, NArray extension and a script below
may help you.  Get NArray from:
  http://www.ruby-lang.org/en/raa-list.rhtml?name=NArray
This script uses PGPLOT extension for plotting.
Also you can get it from NArray's page.

Masa Tanaka

--
require 'narray'

class MyStruct

  attr_reader :size

  def initialize(arg)
    case arg
    when String
      raise ArgumentError, "wrong data size" if arg.size%16 != 0
      @size = arg.size/16
      @data = NArray.to_na( arg, NArray::BYTE, 16, @size )
    else
      raise ArgumentError, "not String"
    end
  end

  def tag0
    @data[ 0..3 ,true].to_type_as_binary(NArray::LINT)
  end
  def tag1
    @data[ 4..7 ,true].to_type_as_binary(NArray::LINT)
  end
  def tag2
    @data[ 8..11,true].to_type_as_binary(NArray::LINT)
  end
  def tag3
    @data[12..13,true].to_type_as_binary(NArray::SINT)
  end
  def tag4
    @data[14..15,true].to_type_as_binary(NArray::SINT)
  end
end

if __FILE__ == $0

  fname = $*.shift
  data = MyStruct.new( open(fname,'r').read )

  if require 'pgplot'
    include Pgplot
    x = NArray.sfloat(data.size).indgen!
    pgbeg '/xwin'
    pgsci 1
    pgenv 0, data.size, -300, 300
    pglab "x", "y", "Example"
    pgsci 2
    pgline x, data.tag0
    pgsci 3
    pgline x, data.tag1
    pgsci 4
    pgline x, data.tag2
    pgsci 5
    pgline x, data.tag3
    pgsci 6
    pgline x, data.tag4
  end
end