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     The matherr functions process errors generated by the functions of
     the math library. These functions call the appropriate matherr
     routine whenever an error is detected. The _matherrl function uses
     the 80-bit long double form of arguments and return values.
 
     You can provide a different definition of the matherr functions to
     carry out special error handling.
 
     When an error occurs in a math routine, matherr is called with a
     pointer to an exception type structure (defined in MATH.H) as an
     argument.
 
     The exception structure contains the following elements:
 
     Element               Description
 
     int type              Exception type
     char * name           Name of function where error occurred
     double arg1, arg2     First & second (if any) argument to function
     double retval         Value to be returned by function
 
     The structure member type specifies the type of math error. It is
     one of the following values, defined in MATH.H:
 
     DOMAIN       SING
     OVERFLOW     TLOSS
     PLOSS        UNDERFLOW
 
     The structure member name is a pointer to a null-terminated string
     containing the name of the function that caused the error. The
     structure members <arg1> and <arg2> specify the values that caused
     the error. (If only one argument is given, it is stored in
     <arg1>.)
 
     The default return value for the given error is <retval>. If you
     change the return value, remember that the return value must
     specify whether an error actually occurred.
 
     If matherr returns 0, an error message is displayed and errno is
     set to an appropriate error value. If matherr returns a nonzero
     value, no error message is displayed, and errno remains unchanged.
 
     Return Value
 
     The matherr functions return 0 to indicate an error and nonzero to
     indicate successful corrective action.
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