From: Sergey <gm.vlkv@...>
Date: 2006-04-18T06:19:07+09:00
Subject: Re: a simple RSA

------=_NextPart_000_0177_01C66243.0669DD90
Content-Type: text/plain;
	format=flowed;
	charset="Windows-1252";
	reply-type=response
Content-Transfer-Encoding: 7bit

Please see attached:
- samples with unpack/inject and each_byte use in str_to_num;
  each_byte is faster;
- num_to_str without use of formatting;
- unit test stuff and
- benchmark code

hope these help
regards
Sergey

----- Original Message ----- 
On Monday, April 17, 2006 2:03 PM, Shannon Fang wrote:
> Hi All,
>
> I tried to implement a simple RSA crypto for my work. It seems all works 
> fine, except that I am not satisfied with the code I wrote below:
>
> def str_to_num(s)
>  h = '0x'
>  (0...s.length).each do |i|
>    h += "%02x" % s[i]
>  end
>  eval(h)
> end
>
> def num_to_str(n)
>  s = ''
>  while n > 0 do
>    s = "%c" % (n & 0xFF) + s
>    n = n >> 8
>  end
>  s
> end
>
> These 2 functions convert string to bignum and vise-versa. It works, but I 
> feel there should be better (faster) way to do this.
>
> Could anyone point the way out?
>
> Thanks!
> Shannon

------=_NextPart_000_0177_01C66243.0669DD90
Content-Type: application/octet-stream;
	name="tStrToNum.rb"
Content-Transfer-Encoding: quoted-printable
Content-Disposition: attachment;
	filename="tStrToNum.rb"

#!/bin/ruby -w=0A=
=0A=
def str_to_num str=0A=
    num =3D 0=0A=
    str.each_byte{ |b| num =3D (num<<8)|b }=0A=
    num=0A=
end=0A=
=0A=
def str_u2_num str=0A=
    str.unpack( "C*" ).inject(0){ |v,c| (v<<8)|c }=0A=
end=0A=
=0A=
def num_to_str num=0A=
    res =3D ''=0A=
    while num>0=0A=
        res << (num&0xFF).chr=0A=
        num >>=3D 8=0A=
    end=0A=
    res.reverse!=0A=
end=0A=
=0A=
if $0 =3D=3D __FILE__=0A=
require 'test/unit'=0A=
SL128 =3D (0..127).inject(''){ |v,e| v<<e.chr }=0A=
SH128 =3D (128..255).inject(''){ |v,e| v<<e.chr }=0A=
=0A=
S256 =3D SL128+SH128=0A=
R256 =3D S256.reverse=0A=
=0A=
class TC < Test::Unit::TestCase=0A=
    def test_str_to_num=0A=
        assert_equal 256, str_to_num( "\x01\x00" )=0A=
        (0..255).each{|c|=0A=
            assert_equal c, str_to_num( c.chr )=0A=
            (0..255).each{|h|=0A=
                assert_equal h*256+c, str_to_num( h.chr + c.chr )=0A=
            }=0A=
        }=0A=
    end=0A=
    def test_num_to_str=0A=
        assert_equal "", num_to_str( 0 )=0A=
        assert_equal "\x01\x00", num_to_str( 256 )=0A=
        (1..255).each{|h|=0A=
            (0..255).each{|c|=0A=
                str =3D h.chr + c.chr=0A=
                num =3D h*256+c=0A=
                assert_equal str, num_to_str( num )=0A=
            }=0A=
        }=0A=
    end=0A=
    def test_same_nums=0A=
        assert_equal str_u2_num( SL128 ), str_to_num( SL128 )=0A=
        assert_equal str_u2_num( SH128 ), str_to_num( SH128 )=0A=
        assert_equal str_u2_num( S256 ),  str_to_num( S256 )=0A=
        assert_equal str_u2_num( R256 ),  str_to_num( R256 )=0A=
    end=0A=
    def test_str_num_str=0A=
        assert_equal '\0x01' + SL128, num_to_str( str_to_num( '\0x01' + =
SL128 ) )=0A=
        assert_equal '\0x01' + S256, num_to_str( str_to_num( '\0x01' + =
S256 ) )=0A=
        assert_equal SH128, num_to_str( str_to_num( SH128 ) )=0A=
        assert_equal R256, num_to_str( str_to_num( R256 ) )=0A=
    end=0A=
end=0A=
require 'test/unit/ui/console/testrunner'=0A=
Test::Unit::UI::Console::TestRunner.run( TC )=0A=
=0A=
=0A=
require 'benchmark'=0A=
=0A=
puts '=3D=3D=3D Benchmark string_to_num'=0A=
=0A=
Benchmark::bm(12) do |x|=0A=
    class << x=0A=
        def fire str, count=0A=
            puts "* |String|=3D#{str.size}, repeat: #{count}"=0A=
            self.report( 'unpack:' ){=0A=
                count.times{ str_to_num str }=0A=
            }=0A=
            resnum =3D 0=0A=
            self.report( 'str_to_num:' ){=0A=
                count.times{ str_to_num str }=0A=
            }=0A=
            self.report( 'num_to_str:' ){=0A=
                count.times{ num_to_str resnum }=0A=
            }=0A=
        end=0A=
    end=0A=
    x.fire( "012",           1000000 )=0A=
    x.fire( "0123456789",    100000 )=0A=
    x.fire( R256+S256,       1000 )=0A=
    x.fire( (R256+S256)*100, 1 )=0A=
end=0A=
=0A=
end=0A=
=0A=
=3Dbegin=0A=
908> ruby -w ./tStrToNum.rb=0A=
Loaded suite TC=0A=
Started=0A=
....=0A=
Finished in 7.218 seconds.=0A=
=0A=
4 tests, 131083 assertions, 0 failures, 0 errors=0A=
=3D=3D=3D Benchmark string_to_num=0A=
                  user     system      total        real=0A=
* |String|=3D3, repeat: 1000000=0A=
unpack:       3.750000   0.000000   3.750000 (  3.797000)=0A=
str_to_num:   3.797000   0.000000   3.797000 (  3.828000)=0A=
num_to_str:   1.547000   0.000000   1.547000 (  1.594000)=0A=
* |String|=3D10, repeat: 100000=0A=
unpack:       3.797000   0.000000   3.797000 (  3.844000)=0A=
str_to_num:   3.812000   0.000000   3.812000 (  3.890000)=0A=
num_to_str:   0.172000   0.000000   0.172000 (  0.204000)=0A=
* |String|=3D512, repeat: 1000=0A=
unpack:       3.109000   0.000000   3.109000 (  3.171000)=0A=
str_to_num:   3.078000   0.000000   3.078000 (  3.172000)=0A=
num_to_str:   0.016000   0.000000   0.016000 (  0.016000)=0A=
* |String|=3D51200, repeat: 1=0A=
unpack:       4.656000   0.031000   4.687000 (  4.734000)=0A=
str_to_num:   4.407000   0.016000   4.423000 (  4.500000)=0A=
num_to_str:   0.000000   0.000000   0.000000 (  0.000000)=0A=
=3Dend=0A=

------=_NextPart_000_0177_01C66243.0669DD90--