TGAMMA(3) Library Functions Manual TGAMMA(3)

tgamma tgammaf tgammal — compute gamma() function

#include <math.h>

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

[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2008 defers to the ISO C standard.

These functions shall compute the gamma () function of x.

An application wishing to check for error situations should set errno to zero and call (FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or (FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

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

If x is a negative integer, a [CX] domain error may occur and either a NaN (if supported) or an implementation-defined value shall be returned. [MX] On systems that support the IEC 60559 Floating-Point option, a domain error shall occur and a NaN shall be returned.

If x is ±0, tgamma (), tgammaf (), and tgammal () shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively. [MX] On systems that support the IEC 60559 Floating-Point option, a pole error shall occur; otherwise, a [CX] pole error may occur.

If the correct value would cause overflow, a range error shall occur and tgamma (), tgammaf (), and tgammal () shall return ±HUGE_VAL, ±HUGE_VALF, or ±HUGE_VALL, respectively, with the same sign as the correct value of the function.

[MX] If x is NaN, a NaN shall be returned.

If x is +Inf, x shall be returned.

If x is -Inf, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.

These functions shall fail if:

[MX] The value of x is a negative integer, or x is -Inf.

If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

[MX] The value of x is zero.

If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be raised.

The value overflows. If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the overflow floating-point exception shall be raised.

These functions may fail if:

The value of x is a negative integer.

If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.

The value of x is zero.

If the integer expression ( math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [ERANGE]. If the integer expression ( math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be raised.

None.

For IEEE Std 754-1985 , overflow happens when 0 < x < 1/DBL_MAX, and 171.7 < x.

On error, the expressions ( math_errhandling & MATH_ERRNO) and ( math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.

This function is named tgamma () in order to avoid conflicts with the historical gamma () and lgamma(3) functions.

It is possible that the error response for a negative integer argument may be changed to a pole error and a return value of ±Inf.

feclearexcept(3) , fetestexcept(3) , lgamma(3)

XBD V1_chap04(7) , <math.h>

First released in Issue 6. Derived from the ISO/IEC 9899:1999 (“ISO C99”) standard.

IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 1-2002, item XSH/TC1/D6/65 is applied, correcting the third paragraph in the RETURN VALUE section.

ISO/IEC 9899:1999 (“ISO C99”) standard, Technical Corrigendum 2 #52 (SD5-XSH-ERN-85) is applied.

January 1, 2008 posix.fail