log$m (2) --- calculate logarithm to the base 10         04/27/83


          | _C_a_l_l_i_n_g _I_n_f_o_r_m_a_t_i_o_n

          |      longreal function log$m (x)
          |      real x

          |      Library: vswtmath (Subsystem mathematical library)


          | _F_u_n_c_t_i_o_n

          |      This  function  implements  the  common  logarithm (base 10)
          |      function.  Arguments must be greater than zero.  The  condi-
          |      tion  SWT_MATH_ERROR$  is  signalled if there is an argument
          |      error.  An on-unit can be  established  to  deal  with  this
          |      error; the SWT Math Library contains a default handler named
          |      'err$m'  which the user may utilize.  If an error is signal-
          |      led due to an invalid argument the default return is the log
          |      of the absolute value of the argument, or zero in  the  case
          |      of a zero argument.

          |      This  function  is  intended  to serve as a single precision
          |      function although it returns a double precision result.  The
          |      function has been coded so that any value returned will  not
          |      overflow  or  underflow  a  single  precision floating point
          |      value.  The double precision register  overlaps  the  single
          |      precision register so it is possible to declare and use this
          |      function as simply a "real" function.


          | _I_m_p_l_e_m_e_n_t_a_t_i_o_n

          |      The algorithm involved uses a minimax rational approximation
          |      on  a  reduction  of the argument.  All positive inputs will
          |      return a valid result.  It is  adapted  from  the  algorithm
          |      given  in  the  book  _S_o_f_t_w_a_r_e  _M_a_n_u_a_l  _f_o_r  _t_h_e  _E_l_e_m_e_n_t_a_r_y
          |      _F_u_n_c_t_i_o_n_s by William Waite and William Cody, Jr.  (Prentice-
          |      Hall, 1980).


          | _C_a_l_l_s

          |      Primos signl$


          | _S_e_e _A_l_s_o

          |      dlog$m (2), err$m (2),
          |      _S_W_T _M_a_t_h _L_i_b_r_a_r_y _U_s_e_r_'_s _G_u_i_d_e










            log$m (2)                     - 1 -                     log$m (2)