man pages section 3: Extended Library Functions, Volume 2
Updated: July 2014

## tgammal(3M)

### Name

tgamma, tgammaf, tgammal - compute gamma function

### Synopsis

```c99 [ flag... ] file... –lm [ library... ]
#include <math.h>

double tgamma(double x);```
`float tgammaf(float x);`
`long double tgammal(long double x);`

### Description

These functions compute the gamma() function of x.

### Return Values

Upon successful completion, these functions return gamma(x).

If x is a negative integer, a domain error occurs and a NaN is returned.

If the correct value would cause overflow, a range error occurs and tgamma(), tgammaf(), and tgammal() return the value of the macro ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL, respectively.

If x is NaN, a NaN is returned.

If x is ±Inf, x is returned.

If x is ±0, a pole error occurs and tgamma(), tgammaf(), and tgammal() return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively.

If x is +Inf, a domain error occurs and a NaN is returned.

### Errors

These functions will fail if:

Domain Error

The value of x is a negative integer or x is −Inf.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception is raised.

Pole Error

The value of x is zero.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide–by-zero floating-point exception is raised.

Range Error

The value overflows.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception is raised.

### Usage

An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

### Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
MT-Safe
Standard