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## 1 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`. See System Calls, 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`.