# tgamma(), tgammaf(), tgammal()

Compute the gamma function of a number

## Synopsis:

```#include <math.h>

double tgamma( double x );

float tgammaf( float x );

long double tgammal( long double x );
```

## Arguments:

x
An arbitrary number.

## Library:

libm

Use the -l m option to qcc to link against this library.

## Description:

The tgamma(), tgammaf(), and tgammal() functions compute Γ(x), which is defined as follows:

To check for error situations, use feclearexcept() and fetestexcept():

• Call feclearexcept(FE_ALL_EXCEPT) before calling tgamma(), tgammaf(), or tgammal().
• On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is nonzero, then an error has occurred.

## Returns:

The gamma of x.

• If x is a negative integer, a domain error may occur and a NaN is returned.
• If x is ±0, these functions return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively. A pole error may occur.
• If the correct value would cause an overflow, a range error occurs and these functions return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively, with the same sign as the correct value of the function.
• If the correct value would cause underflow, and isn't representable, a range error may occur, and these functions return 0.0, or (if IEC 60559 Floating-Point isn't supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.
• If the correct value would cause underflow, and is representable, a range error may occur, and the correct value is returned.
• If x is subnormal and 1 / x is representable, 1 / x is returned.
• If x is NaN, a NaN is returned.
• If x is +Inf, x is returned.
• If x is -Inf, a domain error occurs, and a NaN is returned.

## Errors:

FE_DIVBYZERO
The x argument is 0.
FE_INVALID
The value of x argument is a negative integer, or x is -Inf.
FE_OVERFLOW
The result would cause an overflow.
FE_UNDERFLOW
The value of x isn't equal to y, and the correct function value is subnormal, zero, or underflows.

## Classification:

Safety:
Cancellation point No
Interrupt handler No
Signal handler No