IEEE Std 1003.1-2008, 2016 Edition

Copyright © 2001-2016 The IEEE and The Open Group

tan, tanf, tanl - tangent function

#include <math.h>

double tan(doublex);

float tanf(floatx);

long double tanl(long doublex);

^{[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 tangent of their argument

x, measured in radians.An application wishing to check for error situations should set

errnoto zero and callfeclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.

Upon successful completion, these functions shall return the tangent of

x.If the correct value would cause underflow,

^{[MXX]}and is not representable, a range error may occur, andtan(),tanf(), andtanl() shall return^{[MXX]}0.0, or (if IEC 60559 Floating-Point is not supported) an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.

^{[MX]}Ifxis NaN, a NaN shall be returned.If

xis ±0,xshall be returned.If

xis subnormal, a range error may occur

^{[MXX]}andxshould be returned.

^{[MX]}Ifxis not returned,tan(),tanf(), andtanl() shall return an implementation-defined value no greater in magnitude than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.If

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

^{[MXX]}If the correct value would cause underflow, and is representable, a range error may occur and the correct value shall be returned.

^{[XSI]}If the correct value would cause overflow, a range error shall occur andtan(),tanf(), andtanl() shall return ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL, respectively, with the same sign as the correct value of the function.

These functions shall fail if:

- Domain Error
^{[MX]}The value ofxis ±Inf.If the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall be set to [EDOM]. If the integer expression (math_errhandling& MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.- Range Error
^{[XSI]}The result overflowsIf the integer expression (

math_errhandling& MATH_ERRNO) is non-zero, thenerrnoshall 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:

- Range Error
- The result underflows,
^{[MX]}or the value ofxis subnormal.If the integer expression (

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

## Taking the Tangent of a 45-Degree Angle

#include <math.h> ... double radians = 45.0 * M_PI / 180; double result; ... result = tan (radians);

There are no known floating-point representations such that for a normal argument,

tan(x) is either overflow or underflow.These functions may lose accuracy when their argument is near a multiple of /2 or is far from 0.0.

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.

None.

None.

atan,feclearexcept,fetestexcept,isnanXBD

Treatment of Error Conditions for Mathematical Functions,<math.h>

First released in Issue 1. Derived from Issue 1 of the SVID.

The last two paragraphs of the DESCRIPTION were included as APPLICATION USAGE notes in previous issues.

The

tanf() andtanl() functions are added for alignment with the ISO/IEC 9899:1999 standard.The DESCRIPTION, RETURN VALUE, ERRORS, and APPLICATION USAGE sections are revised to align with the ISO/IEC 9899:1999 standard.

IEC 60559:1989 standard floating-point extensions over the ISO/IEC 9899:1999 standard are marked.

IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/64 is applied, correcting the last paragraph in the RETURN VALUE section.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0635 [68], XSH/TC1-2008/0636 [68], and XSH/TC1-2008/0637 [68] are applied.

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