'\" et
.TH TAN "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.

.SH NAME
tan,
tanf,
tanl
\(em tangent function
.SH SYNOPSIS
.LP
.nf
#include <math.h>
.P
double tan(double \fIx\fP);
float tanf(float \fIx\fP);
long double tanl(long double \fIx\fP);
.fi
.SH DESCRIPTION
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\(hy2008 defers to the ISO\ C standard.
.P
These functions shall compute the tangent of their argument
.IR x ,
measured in radians.
.P
An application wishing to check for error situations should set
.IR errno
to zero and call
.IR feclearexcept (FE_ALL_EXCEPT)
before calling these functions. On return, if
.IR errno
is non-zero or \fIfetestexcept\fR(FE_INVALID | FE_DIVBYZERO |
FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
.SH "RETURN VALUE"
Upon successful completion, these functions shall return the tangent of
.IR x .
.P
If the correct value would cause underflow,
and is not representable,
a range error may occur, and
\fItan\fR(),
\fItanf\fR(),
and
\fItanl\fR()
shall return
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.
.P
If
.IR x
is NaN, a NaN shall be returned.
.P
If
.IR x
is \(+-0,
.IR x
shall be returned.
.P
If
.IR x
is subnormal, a range error may occur
.br
and
.IR x
should be returned.
.P
If
.IR x
is not returned,
\fItan\fR(),
\fItanf\fR(),
and
\fItanl\fR()
shall return an implementation-defined value no greater in magnitude
than DBL_MIN, FLT_MIN, and LDBL_MIN, respectively.
.P
If
.IR x
is \(+-Inf, a domain error shall occur, and either a NaN (if
supported), or an implementation-defined value shall be returned.
.P
If the correct value would cause underflow, and is representable,
a range error may occur and the correct value shall be returned.
.P
If the correct value would cause overflow, a range error shall occur
and
\fItan\fR(),
\fItanf\fR(),
and
\fItanl\fR()
shall return \(+-HUGE_VAL, \(+-HUGE_VALF, and \(+-HUGE_VALL,
respectively, with the same sign as the correct value of the function.
.SH ERRORS
These functions shall fail if:
.IP "Domain\ Error" 12
The value of
.IR x
is \(+-Inf.
.RS 12 
.P
If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
non-zero, then
.IR errno
shall be set to
.BR [EDOM] .
If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
non-zero, then the invalid floating-point exception shall be raised.
.RE
.IP "Range\ Error" 12
The result overflows
.RS 12 
.P
If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
non-zero, then
.IR errno
shall be set to
.BR [ERANGE] .
If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
non-zero, then the overflow floating-point exception shall be raised.
.RE
.br
.P
These functions may fail if:
.IP "Range\ Error" 12
The result underflows,
or the value of
.IR x
is subnormal.
.RS 12 
.P
If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
non-zero, then
.IR errno
shall be set to
.BR [ERANGE] .
If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
non-zero, then the underflow floating-point exception shall be raised.
.RE
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Taking the Tangent of a 45-Degree Angle"
.sp
.RS 4
.nf
\fB
#include <math.h>
\&...
double radians = 45.0 * M_PI / 180;
double result;
\&...
result = tan (radians);
.fi \fR
.P
.RE
.SH "APPLICATION USAGE"
There are no known floating-point representations such that for a
normal argument,
.IR tan (\c
.IR x )
is either overflow or underflow.
.P
These functions may lose accuracy when their argument is near a
multiple of \(*p/2 or is far from 0.0.
.P
On error, the expressions (\fImath_errhandling\fR & MATH_ERRNO) and
(\fImath_errhandling\fR & MATH_ERREXCEPT) are independent of each
other, but at least one of them must be non-zero.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIatan\fR\^(\|)",
.IR "\fIfeclearexcept\fR\^(\|)",
.IR "\fIfetestexcept\fR\^(\|)",
.IR "\fIisnan\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "Section 4.19" ", " "Treatment of Error Conditions for Mathematical Functions",
.IR "\fB<math.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .

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