#! /usr/bin/env python
#
def lcrg_evaluate ( a, b, c, x ):

#*****************************************************************************80
#
## LCRG_EVALUATE evaluates an LCRG, y = ( A * x + B ) mod C.
#
#  Discussion:
#
#    This routine cannot be recommended for production use.  Because we want
#    to do modular arithmetic, but the base is not a power of 2, we need to
#    use "double precision" integers to keep accuracy.
#
#    If we knew the base C, we could try to avoid overflow while not changing
#    precision.
#
#    If the base C was a power of 2, we could rely on the usual properties of
#    integer arithmetic on computers, in which overflow bits, which are always
#    ignored, don't actually matter.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    05 April 2013
#
#  Author:
#
#    John Burkardt
#
#  Parameters:
#
#    Input, integer A, the multiplier for the LCRG.
#
#    Input, integer B, the added value for the LCRG.
#
#    Input, integer C, the base for the modular arithmetic.
#    For 32 bit arithmetic, this is often 2^31 - 1, or 2147483647.  It is
#    required that 0 < C.
#
#    Input, integer X, the value to be processed.
#
#    Output, integer Y, the processed value.
#
  y = ( ( a * x + b ) % c )

  if ( y < 0 ):
    y = y + c

  return y