Liren Large Software Subsidy 7/07.iso/c/c082_144/1.ddi/MATHSRC.ZIP/MATHERRL.C

C/C++ Source or Header | 1992-06-10 | 5.2 KB | 146 lines

/*------------------------------------------------------------------------
 * filename - matherrl.c
 *
 * function(s)
 *        _matherrl - user-modifiable long double math error handler
 *-----------------------------------------------------------------------*/

/*
 *      C/C++ Run Time Library - Version 5.0
 *
 *      Copyright (c) 1987, 1992 by Borland International
 *      All Rights Reserved.
 *
 */


#include <math.h>

#ifdef _Windows
#include <_win.h>
#endif

#ifdef  UNIX__matherrl
#include <stdio.h>
#include <process.h>

char *whyS [] =
{
    "argument domain error",
    "argument singularity ",
    "overflow range error ",
    "underflow range error",
    "total loss of significance",
    "partial loss of significance"
};

/*------------------------------------------------------------------------*

Name            _matherrl - user-modifiable long double math error handler

Usage           #include <math.h>
                int _matherrl(struct _exceptionl *e);

Prototype in    math.h

Description     When  exceptions are  detected in  the long double math
                library then a call is made to __matherrl() with all of
                the available information.

                That function does very little, except to map the exception
                "why"  into either  ERANGE or  EDOMAIN in  errno. Its  main
                purpose is  to act as  a focal point  for changes in  error
                handling.

                For example,  if you were  writing a spreadsheet  you might
                replace  this function with one which pops up an error
                window explaining something like:

                        "logl (-2.0) caused domain error, in cell J7"

                and then longjmp() to a  reset state in the spreadsheet and
                await the next command from the user.

                The default version  of Turbo C's _matherrl routine masks
                underflow and precision errors; others errors are considered
                fatal.  It serves as a hook that you can replace when
                writing your own math error handling routine.

                The rationale for masking underflow and precision errors
                is that these are not errors according to the ANSI C spec.
                Consequently, you will get
                        expl(-1000) = 0
                        sinl(1e100) = NAN
                without any error or warning, even though there is a total
                loss of precision in both cases.  You can trap these errors
                by modifying _matherrl.

                The possible errors are
                        DOMAIN, SING, OVERFLOW, UNDERFLOW, TLOSS, PLOSS
                and listed in <math.h>.  As explained above, UNDERFLOW and
                TLOSS are masked by the default _matherrl.  PLOSS is not
                supported by TC and is not generated by any library functions.
                The remaining errors, DOMAIN, SING, and OVERFLOW, are fatal
                with the default _matherrl.

                You  can  modify  _matherrl  to  be  a  custom error handling
                routine (such as one that catches and resolves certain type
                of  errors); the  modified _matherrl  should return  0 if  it
                failed to resolve  the error, or non-zero if  the error was
                resolved. When _matherrl returns non-zero, no  error message
                is printed, and errno is not changed.

                The  important thing  is  that  we  don't  know what error
                handling you want, but you are assured that all errors will
                arrive at  _matherrl() with all  the information you  need to
                design a custom format.

Return value    The default return  value for _matherrl is simply  0.
                _matherrl can also modify  e->retval, which propagates through
                __matherrl back to the original caller.

                When _matherrl returns 0, (indicating that it was not able to
                resolve the error) __matherrl sets  errno and prints an error
                message.

                When _matherrl returns non-zero, (indicating that it was able
                to resolve the error) errno is not set and no messages are
                printed.

*-------------------------------------------------------------------------*/
int _FARFUNC _matherrl (struct _exceptionl *e)
{
#ifdef _Windows
    char errMsg[ 80 ];
    sprintf (errMsg,
        "%s (%8Lg,%8Lg): %s\n", e->name, e->arg1, e->arg2, whyS [e->type - 1]);
    _errorExitBox( errMsg, 1 );
#else
    fprintf (stderr,
        "%s (%8Lg,%8Lg): %s\n", e->name, e->arg1, e->arg2, whyS [e->type - 1]);

    exit (1);
#endif
}
#else

int _FARFUNC _matherrl(struct _exceptionl *e)
{
        if (e->type == UNDERFLOW)
        {
                /* flush underflow to 0 */
                e->retval = 0;
                return 1;
        }
        if (e->type == TLOSS)
        {
                /* total loss of precision, but ignore the problem */
                return 1;
        }
        /* all other errors are fatal */
        return 0;
}


#endif