lambdaway :: middle

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_h1 middle square method

_p Following [[https://rosettacode.org|https://rosettacode.org/wiki/Pseudo-random_numbers/Middle-square_method]], « to generate a sequence of n-digit pseudo-random numbers, an n-digit starting value is created and squared, producing a 2n-digit number. If the result has fewer than 2n digits, leading zeroes are added to compensate. The middle n digits of the result would be the next number in the sequence and returned as the result. This process is then repeated to generate more numbers. »

_p For instance:

{pre
'{* 675248 675248}
-> {* 675248 675248}  -> floor( 455959861504 / 1000 ) // del 3 lasts
                 -> 455959861 % 1000000          // del 3 firsts
                 -> 959861
'{* 959861 959861}
-> {* 959861 959861}  -> 921(333139)321
and so on...
}

_h2 1) using C

{prewrap
long long seed;
long long random() '{
        seed = seed * seed / 1000 % 1000000;
        return seed;
}
int main() '{
        seed = 675248;
        for(int i=1;i<=5;i++)
                printf("%lld\n",random());
        return 0;
}
Output:
959861 333139 981593 524817 432883
}

_h2 2) using lambdatalk

{prewrap
'{def W.fill
 {lambda {:v :n}
  {if {<= :n 0}
   then
   else :v{W.fill :v {- :n 1}}}}}
-> {def W.fill
 {lambda {:v :n}
  {if {<= :n 0}
   then
   else :v{W.fill :v {- :n 1}}}}}

'{def W.pad
 {lambda {:n :size}
  {if {<= {W.length :n} :size} 
   then :n{W.fill :size {- :size {W.length :n}}}
   else {W.slice 0 {- :size {W.length :n}} :n}}}}
-> {def W.pad
 {lambda {:n :size}
  {if {<= {W.length :n} :size} 
   then :n{W.fill :size {- :size {W.length :n}}}
   else {W.slice 0 {- :size {W.length :n}} :n}}}}

'{def randoms
 {lambda {:s :n}
  {if {>= :n 0}
   then :s
        {randoms {W.pad {% {floor {/ {* :s :s} 1.e3}} 1.e6} 6}
                 {- :n 1}}
   else}}}
-> {def randoms
 {lambda {:s :n}
  {if {>= :n 0}
   then :s {randoms {W.pad {% {floor {/ {* :s :s} 1.e3}} 1.e6} 6}
                    {- :n 1}}
   else}}}

'{randoms 959861 4}
-> {randoms 959861 4}

'{randoms 675248 4}
-> {randoms 675248 4}

675248 '{* 675248 675248} -> {* 675248 675248} 
959861 '{* 959861 959861} -> {* 959861 959861} 
333139 '{* 333139 333139} -> {* 333139 333139}
981593 '{* 981593 981593} -> {* 981593 981593}
524817 ...

'{randoms 675248 300}
-> 
{randoms 675248 300}

713789 '{* 713789 713789} -> {* 713789 713789} = 509[494736]521
}

_p {i alain marty | 2023/01/12}