RosettaCodeData/Task/Lucas-Lehmer-test/FutureBasic/lucas-lehmer-test.basic

// ------------------------------------------------------------
//  Lucas–Lehmer Mersenne prime tester
//  Using FutureBasic 7.0.37
//
//  November 2025, R.W.
// ------------------------------------------------------------

include "gmp.incl"

// ------------------------------------------------------------
//  Lucas–Lehmer Mersenne prime tester
// ------------------------------------------------------------

CFTimeInterval tim

// Global mpz_t bigints reused everywhere
mpz_t ts           // Lucas–Lehmer state ts
mpz_t mp, mp_minus1
mpz_t tmp          // scratch for reduction
unsigned long gN   // last exponent tested (for [Next])
long gCount

// ------------------------------------------------------------
//  Init / clear big integers
// ------------------------------------------------------------
local fn InitBigInts
  long maxBits
  maxBits = 120000    // enough for p up to ~100k
  mpz_init2( ts, maxBits )
  mpz_init2( mp, maxBits )
  mpz_init2( mp_minus1, maxBits )
  mpz_init2( tmp, maxBits )
end fn

local fn ClearBigInts
  mpz_clear( ts )
  mpz_clear( mp )
  mpz_clear( mp_minus1 )
  mpz_clear( tmp )
end fn

// ------------------------------------------------------------
//  Small 32-bit primality test for exponents p
// ------------------------------------------------------------
local fn IsPrime32( n as unsigned long ) as boolean
  unsigned long d
  // quick filter/rejects
  if n  < 2 then return _False
  if n == 2 then return _True
  // even = composite
  if ( n AND 1 ) == 0 then return _False
  d = 3
  while d * d <= n
    if ( n MOD d ) == 0 then return _False
    d = d + 2
  wend
end fn = _true

// ------------------------------------------------------------
//  IsMersennePrime_LL
//  Lucas–Lehmer test for M_p = 2^p − 1
//  Returns _true if M_p is prime
// ------------------------------------------------------------

local fn IsMersennePrime_LL( p as unsigned long ) as boolean
  unsigned long k
  // quick filter/rejects
  if p == 2 then return _True
  if p <  2 then return _False
  // no even exponents (except the handled p = 2)
  if ( p AND 1 ) == 0 then return _False
  // exponent itself must be prime
  if fn IsPrime32( p ) == _false then return _False
  // build M_p = 2^p − 1
  mpz_set_ui( mp_minus1, 1 )
  mpz_mul_2exp( mp_minus1, mp_minus1, p )  // mp_minus1 = 1 << p
  mpz_sub_ui( mp_minus1, mp_minus1, 1 )    // Mp = 2^p - 1
  // Lucas–Lehmer sequence:
  mpz_set_ui( ts, 4 )
  k = 0
  // s = 4; repeat p−2 times: s = s^2 − 2 (mod M_p)
  while k < p - 2
    mpz_mul( ts, ts, ts )           // s = s^2
    mpz_sub_ui( ts, ts, 2 )         // s -= 2
    mpz_mod( ts, ts, mp_minus1 )    // s = s mod M_p
    k++
  wend
  if fn mpz_cmp_ui( ts, 0 ) == 0 then return _True
end fn = _False

// ------------------------------------------------------------
//  LL_More
//  Scan upward from gN until the next M_p is found
// ------------------------------------------------------------

void local fn LL_More
  CFStringRef pline
  boolean     iterating
  unsigned long i

  tim = fn CACurrentMediaTime

  iterating = _true
  // start from the next exponent after gN
  i = gN + 1
  // ensure we start from a valid candidate:
  if i <= 2
    i = 2
  else
    if ( i AND 1 ) == 0
      i++
    end if
  end if

  while iterating
    if fn IsMersennePrime_LL( i )
      gCount++
      //pline = fn StringWithFormat( @"M%lu", i )
      pline = fn StringWithFormat(@"%4lu M%lu", gCount, i)
      print pline;
      printf @" (%.3f secs)", ( fn CACurrentMediaTime - tim )
      iterating = _false
    end if
    // advance to next candidate exponent
    if i == 2
      i = 3
    else
      i = i + 2
    end if
  wend
  // remember last exponent tested so [Next] continues from here
  if i >= 3
    gN = i - 2
  else
    gN = i
  end if
end fn

// ------------------------------------------------------------
//  Compute Mersenne primes up to an initial exponent gN
// ------------------------------------------------------------
local fn Lucas_LehmerMP
  unsigned long i

  fn InitBigInts

  print @"\nMersenne primes found with Lucas–Lehmer:\n"

  // initial exponent limit for the first scan
  gN = 5000
  gCount = 0

  tim = fn CACurrentMediaTime
  // handle p = 2 separately
  if gN >= 2
    gCount++
    i = 2
    printf @"%4lu M%lu", gCount, i
  end if

  // scan odd exponents 3..gN
  i = 3
  while i <= gN
    if fn IsMersennePrime_LL( i )
      gCount++
      printf @"%4lu M%lu", gCount, i
    end if
    i = i + 2
  wend

  printf @"\nElapsed time: %.3f secs", ( fn CACurrentMediaTime - tim )
  print  @"\nClick [Next] for the next exponents.\n"
end fn

// ------------------------------------------------------------
//  Dialog handler
// ------------------------------------------------------------
void local fn DoDialog( ev as long, tag as long, wnd as long, obj as CFTypeRef )
  select ev
    case _btnClick
      select tag
        case 2
          fn LL_More
      end select

    case _windowShouldClose
      fn ClearBigInts
      end
  end select
end fn

on dialog fn DoDialog

// ------------------------------------------------------------
//  Main
// ------------------------------------------------------------
window 1, @"Lucas–Lehmer Test", ( 0, 0, 620, 500 )
button 2, YES,, @"Next", ( 500, 20, 100, 20 ),,, 1

fn Lucas_LehmerMP

HandleEvents

//