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Mathematical Functions (`math.h')

   This chapter groups a wide variety of mathematical functions.  The
corresponding definitions and declarations are in `math.h'.  Two
definitions from `math.h' are of particular interest.
  1. The representation of infinity as a `double' is defined as
     `HUGE_VAL'; this number is returned on overflow by many functions.
  2. The structure `exception' is used when you write customized error
     handlers for the mathematical functions.  You can customize error
     handling for most of these functions by defining your own version
     of `matherr'; see the section on `matherr' for details.
   Since the error handling code calls `fputs', the mathematical
subroutines require stubs or minimal implementations for the same list
of OS subroutines as `fputs': `close', `fstat', `isatty', `lseek',
`read', `sbrk', `write'.  *Note System Calls: (libc.info)syscalls, for
a discussion and for sample minimal implementations of these support
subroutines.
   Alternative declarations of the mathematical functions, which exploit
specific machine capabilities to operate faster--but generally have
less error checking and may reflect additional limitations on some
machines--are available when you include `fastmath.h' instead of
`math.h'.