old/PAS/IsPrime.pas

{IsPrime.Pas ver. 2.0 (c) Max Alekseyev <relf@os2.ru>, 2:5015/60@FidoNet}
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4^(-Rounds).}

const Rounds=20;

function mulmod(x,y,m:longint):longint; assembler;
asm
{$IFDEF USE32}
  mov eax,x
  mul y
  div m
  mov eax,edx
{$ELSE}
  db $66; mov ax,word ptr x
  db $66; mul word ptr y
  db $66; div word ptr m
  mov ax,dx
  db $66; shr dx,16
{$ENDIF}
end;

function powmod(x,a,m:longint):longint;
var r:longint;
begin
  r:=1;
  while a>0 do
  begin
    if odd(a) then r:=mulmod(r,x,m);
    a:=a shr 1;
    x:=mulmod(x,x,m);
  end;
  powmod:=r;
end;

function isprime(p:longint):boolean;
var q,i,a:longint;
begin
if odd(p) and (p>1) then
begin
  isprime:=true;
  q:=p-1;
  repeat q:=q shr 1; until odd(q);
  for i:=1 to Rounds do
  begin
    {$IFDEF USE32} a:=Random(p-2)+2; {$ELSE} a:=2+Trunc(Random*(p-2)); {$ENDIF}
    if powmod(a,p-1,p)<>1 then
    begin
      isprime:=false; break;
    end;
    a:=powmod(a,q,p);
    if a<>1 then
    begin
      while (a<>1) and (a<>p-1) do a:=mulmod(a,a,p);
      if a=1 then
      begin
        isprime:=false; break;
      end;
    end;
  end;
end else isprime:=(p=2);
end;

var t:longint;
begin
  Randomize; {Do not forget to reset Random Generator!}
  for t:=1000000000 to 1000100000 do if isprime(t) then writeln(t);
end.