matherr(3m)															       matherr(3m)

Name
       matherr - error-handling function for System V math library

Syntax
       #include <math.h>

       int matherr (x)
       struct exception *x;

Description
       The  subroutine	is  invoked by functions in the System V Math Library when errors are detected.  Users may define their own procedures for
       handling errors by including a function named in their programs.  The subroutine must be of the form described above.   A  pointer  to  the
       exception  structure x will be passed to the user-supplied function when an error occurs.  This structure, which is defined in the <math.h>
       header file, is as follows:
       struct exception {
	    int type;
	    char *name;
	    double arg1, arg2, retval;
       };

       The element type is an integer describing the type of error that has occurred, from the following list of constants (defined in the  header
       file):
       DOMAIN	  domain error
       SING	  singularity
       OVERFLOW   overflow
       UNDERFLOW  underflow
       TLOSS	  total loss of significance
       PLOSS	  partial loss of significance

       The  element name points to a string containing the name of the function that had the error.  The variables arg1 and arg2 are the arguments
       to the function that had the error.  The retval is a double that is returned by the function having the error.  If  it  supplies  a  return
       value, the user's must return nonzero.  If the default error value is to be returned, the user's must return 0.

       If  is  not  supplied  by the user, the default error-handling procedures, described with the math functions involved, will be invoked upon
       error.  These procedures are also summarized in the table below.  In every case, errno is set to nonzero and the program continues.

Examples
       matherr(x)
       register struct exception *x;
       {
	    switch (x->type) {
	    case DOMAIN:
	    case SING: /* print message and abort */
		 fprintf(stderr, "domain error in %s
", x->name);
		 abort( );
	    case OVERFLOW:
		 if (!strcmp("exp", x->name)) {
		      /* if exp, print message, return the argument */
		      fprintf(stderr, "exp of %f
", x->arg1);
		      x->retval = x->arg1;
		 } else if (!strcmp("sinh", x->name)) {
		      /* if sinh, set errno, return 0 */
		      errno = ERANGE;
		      x->retval = 0;
		 } else
		      /* otherwise, return HUGE */
		      x->retval = HUGE;
		 break;
	    case UNDERFLOW:
		 return(0); /* execute default procedure */
	    case TLOSS:
	    case PLOSS:
		 /* print message and return 0 */
		 fprintf(stderr, "loss of significance in %s
", x->name);
		 x->retval = 0;
		 break;
	    }
	    return(1);
       }

+-------------------------------------------------------------------------------------------------------------------------------------------------+
|		       |				DEFAULT ERROR HANDLING PROCEDURES							  |
|		       |															  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|		       |     Types of Errors	  |		    |			 |			|		  |		  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|		       |	 DOMAIN 	  |	 SING	    |	  OVERFLOW	 |	UNDERFLOW	|     TLOSS	  |	PLOSS	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   BESSEL:	       |	    -		  |	  -	    |	      H 	 |	    0		|      M, 0	  |	  *	  |
|   y0, y1, yn	       |	 M, -H		  |	  -	    |	      - 	 |	    -		|	-	  |	  -	  |
|    (neg. no.)        |			  |		    |			 |			|		  |		  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   EXP:	       |	    -		  |	  -	    |	      H 	 |	    0		|	-	  |		  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   POW:	       |	    -		  |	  -	    |	      H 	 |	    0		|	-	  |	  -	  |
|   (neg.)**(non-      |	  M, 0		  |	  -	    |	      - 	 |	    -		|	-	  |	  -	  |
|    int.), 0**0       |			  |		    |			 |			|		  |		  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   LOG:	       |			  |		    |			 |			|		  |		  |
|   log(0):	       |	    -		  |	M, -H	    |	      - 	 |	    -		|	-	  |	  -	  |
|   log(neg.):	       |	  M, -H 	  |	  -	    |	      - 	 |	    -		|	-	  |	  -	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   SQRT:	       |	  M, 0		  |	  -	    |	      - 	 |	    -		|	-	  |	  -	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   GAMMA:	       |	    -		  |	 M, H	    |	      - 	 |	    -		|	-	  |	  -	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   HYPOT:	       |	    -		  |	  -	    |	      H 	 |	    -		|	-	  |	  -	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   SINH, COSH:        |	    -		  |	  -	    |	      H 	 |	    -		|	-	  |	  -	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   SIN, COS:	       |	    -		  |	  -	    |	      - 	 |	    -		|      M, 0	  |	  *	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   TAN:	       |	    -		  |	  -	    |	      H 	 |	    -		|      M, 0	  |	  *	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
|   ACOS, ASIN:        |	  M, 0		  |	  -	    |	      - 	 |	    -		|	-	  |	  -	  |
+----------------------+--------------------------+-----------------+--------------------+----------------------+-----------------+---------------+
       +----------------------------------------------------+
       |		   ABBREVIATIONS		    |
       | *    As much as possible of the value is returned. |
       | M    Message is printed.			    |
       | H    HUGE is returned. 			    |
       | -H   -HUGE is returned.			    |
       | 0    0 is returned.				    |
       +----------------------------------------------------+

									VAX							       matherr(3m)