4.3BSD-UWisc/man/cat3/infnan.3m

INFNAN(3M)          UNIX Programmer's Manual           INFNAN(3M)



NAME
     infnan - signals invalid floating-point operations on a VAX
     (temporary)

SYNOPSIS
     #include <math.h>

     double infnan(iarg)
     int iarg;

DESCRIPTION
     At some time in the future, some of the useful properties of
     the Infinities and _N_a_Ns in the IEEE standard 754 for Binary
     Floating-Point Arithmetic will be simulated in UNIX on the
     DEC VAX by using its Reserved Operands.  Meanwhile, the
     Invalid, Overflow and Divide-by-Zero exceptions of the IEEE
     standard are being approximated on a VAX by calls to a pro-
     cedure _i_n_f_n_a_n in appropriate places in _l_i_b_m.  When better
     exception-handling is implemented in UNIX, only _i_n_f_n_a_n among
     the codes in _l_i_b_m will have to be changed.  And users of
     _l_i_b_m can design their own _i_n_f_n_a_n now to insulate themselves
     from future changes.

     Whenever an elementary function code in _l_i_b_m has to simulate
     one of the aforementioned IEEE exceptions, it calls
     infnan(iarg) with an appropriate value of _i_a_r_g.  Then a
     reserved operand fault stops computation.  But _i_n_f_n_a_n could
     be replaced by a function with the same name that returns
     some plausible value, assigns an apt value to the global
     variable _e_r_r_n_o, and allows computation to resume.  Alterna-
     tively, the Reserved Operand Fault Handler could be changed
     to respond by returning that plausible value, etc.  instead
     of aborting.

     In the table below, the first two columns show various
     exceptions signaled by the IEEE standard, and the default
     result it prescribes.  The third column shows what value is
     given to _i_a_r_g by functions in _l_i_b_m when they invoke
     infnan(iarg) under analogous circumstances on a VAX.
     Currently _i_n_f_n_a_n stops computation under all those cir-
     cumstances.  The last two columns offer an alternative; they
     suggest a setting for _e_r_r_n_o and a value for a revised _i_n_f_n_a_n
     to return.  And a C program to implement that suggestion
     follows.
9          IEEE      IEEE
          Signal    Default   _i_a_r_g    _e_r_r_n_o             _i_n_f_n_a_n
          __________________________________________________
          Invalid   _N_a_N       EDOM    EDOM              0
          Overflow  +_Infinity ERANGE  ERANGE            HUGE
          Div-by-0  +_Infinity +_ERANGE ERANGE or EDOM    +_HUGE
9                    (HUGE = 1.7e38 ... nearly  2.0**127)



Printed 12/27/86          May 27, 1986                          1






INFNAN(3M)          UNIX Programmer's Manual           INFNAN(3M)



     ALTERNATIVE  _i_n_f_n_a_n:
9     #include   <math.h>
     #include   <errno.h>
     extern int errno ;
     double     infnan(iarg)
     int        iarg ;
     {
                switch(iarg) {
                case      ERANGE: errno = ERANGE; return(HUGE);
                case     -ERANGE: errno = EDOM;   return(-HUGE);
                default:          errno = EDOM;   return(0);
                }
     }

SEE ALSO
     math(3M), intro(2), signal(3).

     ERANGE and EDOM are defined in <errno.h>.  See intro(2) for
     explanation of EDOM and ERANGE.
































9


Printed 12/27/86          May 27, 1986                          2