#! /usr/bin/env python
#
def i4_seed_advance ( seed ) :

#*****************************************************************************80
#
## I4_SEED_ADVANCE "advances" the seed.
#
#  Discussion:
#
#    This routine implements one step of the recursion
#
#      SEED = ( 16807 * SEED ) mod ( 2^31 - 1 )
#
#    This version of the routine does not check whether the input value of
#    SEED is zero.  If the input value is zero, the output value will be zero.
#
#    If we repeatedly use the output of SEED_ADVANCE as the next input,
#    and we start with SEED = 12345, then the first few iterates are:
#
#         Input      Output
#          SEED        SEED
#
#         12345   207482415
#     207482415  1790989824
#    1790989824  2035175616
#    2035175616    77048696
#      77048696    24794531
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    05 April 2013
#
#  Author:
#
#    John Burkardt
#
#  Reference:
#
#    Paul Bratley, Bennett Fox, Linus Schrage,
#    A Guide to Simulation,
#    Second Edition,
#    Springer, 1987,
#    ISBN: 0387964673,
#    LC: QA76.9.C65.B73.
#
#    Bennett Fox,
#    Algorithm 647:
#    Implementation and Relative Efficiency of Quasirandom
#    Sequence Generators,
#    ACM Transactions on Mathematical Software,
#    Volume 12, Number 4, December 1986, pages 362-376.
#
#    Pierre L'Ecuyer,
#    Random Number Generation,
#    in Handbook of Simulation,
#    edited by Jerry Banks,
#    Wiley, 1998,
#    ISBN: 0471134031,
#    LC: T57.62.H37.
#
#    Peter Lewis, Allen Goodman, James Miller,
#    A Pseudo-Random Number Generator for the System/360,
#    IBM Systems Journal,
#    Volume 8, Number 2, 1969, pages 136-143.
#
#  Parameters:
#
#    Input, integer SEED, the seed value.
#
#    Output, integer SEED, the "next" seed.
#
  from sys import exit

  i4_huge = 2147483647

  seed = ( seed % i4_huge )

  if ( seed < 0 ):
    seed = seed + i4_huge

  if ( seed == 0 ):
    print ( '' )
    print ( 'I4_ADVANCE_SEED - Fatal error!' )
    print ( '  Input SEED = 0!' )
    exit ( 'I4_ADVANCE_SEED - Fatal error!' )

  k = ( seed // 127773 )

  seed = 16807 * ( seed - k * 127773 ) - k * 2836

  if ( seed < 0 ):
    seed = seed + i4_huge

  return seed

def i4_seed_advance_test ( ):

#*****************************************************************************80
#
## I4_SEED_ADVANCE_TEST tests I4_SEED_ADVANCE.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    05 April 2013
#
#  Author:
#
#    John Burkardt
#
  import platform

  print ( '' )
  print ( 'I4_SEED_ADVANCE_TEST' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  I4_SEED_ADVANCE advances the seed.' )
  print ( '' )
  print ( '  Step        SEED input       SEED output' )
  print ( '' )

  seed_new = 12345

  for step in range ( 1, 11 ):

    seed = seed_new
    seed_new = i4_seed_advance ( seed )

    print ( '  %4d  %16d  %16d' % ( step, seed, seed_new ) )
#
#  Terminate.
#
  print ( '' )
  print ( 'I4_SEED_ADVANCE_TEST:' )
  print ( '  Normal end of execution.' )
  return

if ( __name__ == '__main__' ):
  from timestamp import timestamp
  timestamp ( )
  i4_seed_advance_test ( )
  timestamp ( )