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.TH LOG1P 3M "Jul 12, 2006" "SunOS 5.11" "Mathematical Library Functions"
.SH NAME
log1p, log1pf, log1pl \- compute natural logarithm
.SH SYNOPSIS
.LP
.nf
c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ]
#include <math.h>

\fBdouble\fR \fBlog1p\fR(\fBdouble\fR \fIx\fR);
.fi

.LP
.nf
\fBfloat\fR \fBlog1pf\fR(\fBfloat\fR \fIx\fR);
.fi

.LP
.nf
\fBlong double\fR \fBlog1pl\fR(\fBlong double\fR \fIx\fR);
.fi

.SH DESCRIPTION
.sp
.LP
These functions compute log(e)(1.0 + \fIx\fR).
.SH RETURN VALUES
.sp
.LP
Upon successful completion, these functions return the natural logarithm of 1.0
+ \fIx\fR.
.sp
.LP
If \fIx\fR is \(mi1, a pole error occurs and \fBlog1p()\fR, \fBlog1pf()\fR, and
\fBlog1pl()\fR return \(mi\fBHUGE_VAL\fR, \(mi\fBHUGE_VALF\fR, and
\(mi\fBHUGE_VALL\fR, respectively.
.sp
.LP
For finite values of \fIx\fR that are less than \(mi1, or if \fIx\fR is
\(miInf, a domain error occurs and a NaN is returned.
.sp
.LP
If \fIx\fR is NaN, a NaN is returned.
.sp
.LP
If \fIx\fR is \(+-0 or +Inf, \fIx\fR is returned.
.sp
.LP
For exceptional cases, \fBmatherr\fR(3M) tabulates the values to be returned by
\fBlog1p()\fR as specified by SVID3 and XPG3.
.SH ERRORS
.sp
.LP
These functions will fail if:
.sp
.ne 2
.mk
.na
\fBDomain Error\fR
.ad
.RS 16n
.rt
The finite value of \fIx\fR is less than \(mi1, or \fIx\fR is -Inf.
.sp
If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is
non-zero, the invalid floating-point exception is raised.
.sp
The \fBlog1p()\fR function sets \fBerrno\fR to \fBEDOM\fR if the value of
\fIx\fR is less than \(mi1.
.RE

.sp
.ne 2
.mk
.na
\fBPole Error\fR
.ad
.RS 16n
.rt
The value of \fIx\fR is \(mi1.
.sp
If the integer expression (\fBmath_errhandling\fR & \fBMATH_ERREXCEPT\fR) is
non-zero, the divide-by-zero floating-point exception is raised.
.RE

.SH USAGE
.sp
.LP
An application wanting to check for exceptions should call
\fBfeclearexcept\fR(\fBFE_ALL_EXCEPT\fR) before calling these functions. On
return, if \fBfetestexcept\fR(\fBFE_INVALID\fR | \fBFE_DIVBYZERO\fR |
\fBFE_OVERFLOW\fR | \fBFE_UNDERFLOW\fR) 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.
.sp
.LP
An application can also set \fBerrno\fR to 0 before calling \fBlog1p()\fR. On
return, if \fBerrno\fR is non-zero, an error has occurred. The \fBlog1pf()\fR
and \fBlog1pl()\fR functions do not set \fBerrno\fR.
.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
tab(	) box;
cw(2.75i) |cw(2.75i)
lw(2.75i) |lw(2.75i)
.
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.sp
.LP
.BR math.h (3HEAD),
.BR feclearexcept (3M),
.BR fetestexcept (3M),
.BR log (3M),
.BR matherr (3M),
.BR attributes (7),
.BR standards (7)