function [ s, j, k, l ] = i4_mant ( x )

%*****************************************************************************80
%
%% I4_MANT computes the "mantissa" of an R8.
%
%  Discussion:
%
%    This routine computes the "mantissa" or "fraction part" of a real
%    number X, which it stores as a pair of integers, (J/K).
%
%    It also computes the sign, and the integer part of the logarithm
%    (base 2) of X.
%
%    On return:
%
%      X = S * (J/K) * 2^L
%
%    where
%
%      S is +1 or -1,
%      K is a power of 2,
%      1 <= (J/K) < 2,
%      L is an integer.
%
%  Licensing:
%
%    This code is distributed under the GNU LGPL license.
%
%  Modified:
%
%    04 November 2005
%
%  Author:
%
%    John Burkardt
%
%  Parameters:
%
%    Input, real X, the number to be decomposed.
%
%    Output, integer S, the "sign" of the number.
%    S will be -1 if X is less than 0, and +1 if X is greater
%    than or equal to zero.
%
%    Output, integer J, the top part of the mantissa fraction.
%
%    Output, integer K, the bottom part of the mantissa
%    fraction.  K is a power of 2.
%
%    Output, integer L, the integer part of the logarithm (base 2) of X.
%

%
%  1: Handle the special case of 0.
%
  if ( x == 0.0 )
    s = 1;
    j = 0;
    k = 1;
    l = 0;
    return
  end
%
%  2: Determine the sign S.
%
  if ( 0.0 < x )
    s = 1;
  else
    s = -1;
    x = -x;
  end
%
%  3: Force X to lie between 1 and 2, and compute the logarithm L.
%
  l = 0;

  while ( 2.0 <= x )
    x = x / 2.0;
    l = l + 1;
  end

  while ( x < 1.0 )
    x = x * 2.0;
    l = l - 1;
  end
%
%  4: Now strip out the mantissa as J/K.
%
  j = 0;
  k = 1;

  while ( 1 )

    j = 2 * j;

    if ( 1.0 <= x )
      j = j + 1;
      x = x - 1.0;
    end

    if ( x == 0.0 )
      break
    end

    k = 2 * k;
    x = x * 2.0;

  end

  return
end
