Re: lun - Lucky Number

Marcel Logen <333200007110-0201@ybtra.de> wrote:

Rich in sci.crypt:
 

Ok, here's a simple random number generator using /dev/urandom:
>
   #!/usr/bin/tclsh
>
   set fd [open /dev/urandom {RDONLY BINARY}]
   binary scan [read $fd 16] ww hi lo
   close $fd
>
   puts "Your 128-bit random number is: [expr {abs($hi)*2^64 + abs($lo)}]"

 
Interesting. But what is "ww"?

Partially an attempt to make an unspoken point.  For those of us who
don't know go, reading go code can leave us /wondering/ what's going on
(at least until we dig into the go docs enough to figure it out).

The real explanation is it is the Tcl binary command operator for
"convert 8 bytes into a signed 64-bit integer".  In which case I
suspect "w" was chosen to be short for (w)ide.

The two w's in a row convert consequitive 8 bytes into unsigned
64-bit integers, storing the first into variable "hi" and the second
into variable lo.

Then the [expr] call converts hi and lo into a single longer integer
(which, thinking about it now, since I have to abs() them, means this
is really outputting a 126 bit value instead.

16 * 8 = 128 -> OK, but ...:
 

Four sample runs:
>
   ~$ ./random.tcl
   Your 128-bit random number is: 12845925169244013330
   ~$ ./random.tcl
   Your 128-bit random number is: 12267131317558982811
   ~$ ./random.tcl
   Your 128-bit random number is: 10434877321040400260
   ~$ ./random.tcl
   Your 128-bit random number is: 16618556391581443091

          ^^^
             64 (?)
 
| $ echo 'l(16618556391581443091)/l(2)' | bc -l
| 63.84942886744934185453
 
But I'm not entirely sure if I'm on the right track.

Ugh..., no, you are right.  ^ is xor.  ** is power.  The code should be:

    #!/usr/bin/tclsh

    set fd [open /dev/urandom {RDONLY BINARY}]
    binary scan [read $fd 16] ww hi lo
    close $fd

    puts "Your 126-bit random number is: [expr {abs($hi)*2**64 + abs($lo)}]"



    ~$ ./random.tcl
    Your 126-bit random number is: 169336852709816669373259866667412280949
    ~$ ./random.tcl
    Your 126-bit random number is: 32633310813732482344192030424429288689
    ~$ ./random.tcl
    Your 126-bit random number is: 76929973179533891725985594329257253768
    ~$ ./random.tcl
    Your 126-bit random number is: 49046152244045834428660372315683579977


   ~$  echo 'l(49046152244045834428660372315683579977)/l(2)' | bc -l
    125.20547946978097462900

or

    ~$ echo 'l(169336852709816669373259866667412280949)/l(2)' | bc -l
    126.99316358625335794390