| .\" Copyright 1995 Jim Van Zandt <jrv@vanzandt.mv.com> |
| .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk |
| .\" <mtk.manpages@gmail.com> |
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| .\" Modified 2002-07-27 by Walter Harms |
| .\" (walter.harms@informatik.uni-oldenburg.de) |
| .TH LOG1P 3 2017-09-15 "" "Linux Programmer's Manual" |
| .SH NAME |
| log1p, log1pf, log1pl \- logarithm of 1 plus argument |
| .SH SYNOPSIS |
| .nf |
| .B #include <math.h> |
| .PP |
| .BI "double log1p(double " x ); |
| .BI "float log1pf(float " x ); |
| .BI "long double log1pl(long double " x ); |
| .PP |
| .fi |
| Link with \fI\-lm\fP. |
| .PP |
| .in -4n |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .in |
| .PP |
| .ad l |
| .BR log1p (): |
| .RS 4 |
| _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L |
| || _XOPEN_SOURCE\ >=\ 500 |
| .\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .RE |
| .br |
| .BR log1pf (), |
| .BR log1pl (): |
| .RS 4 |
| _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L |
| || /* Since glibc 2.19: */ _DEFAULT_SOURCE |
| || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE |
| .RE |
| .ad b |
| .SH DESCRIPTION |
| These functions return a value equivalent to |
| .PP |
| .nf |
| log (1 + \fIx\fP) |
| .fi |
| .PP |
| The result is computed in a way |
| that is accurate even if the value of |
| .I x |
| is near zero. |
| .SH RETURN VALUE |
| On success, these functions return the natural logarithm of |
| .IR "(1\ +\ x)" . |
| .PP |
| If |
| .I x |
| is a NaN, |
| a NaN is returned. |
| .PP |
| If |
| .I x |
| is positive infinity, positive infinity is returned. |
| .PP |
| If |
| .I x |
| is \-1, a pole error occurs, |
| and the functions return |
| .RB - HUGE_VAL , |
| .RB - HUGE_VALF , |
| or |
| .RB - HUGE_VALL , |
| respectively. |
| .PP |
| If |
| .I x |
| is less than \-1 (including negative infinity), |
| a domain error occurs, |
| and a NaN (not a number) is returned. |
| .\" POSIX.1 specifies a possible range error if x is subnormal |
| .\" glibc 2.8 doesn't do this |
| .SH ERRORS |
| See |
| .BR math_error (7) |
| for information on how to determine whether an error has occurred |
| when calling these functions. |
| .PP |
| The following errors can occur: |
| .TP |
| Domain error: \fIx\fP is less than \-1 |
| .I errno |
| is set to |
| .BR EDOM |
| (but see BUGS). |
| An invalid floating-point exception |
| .RB ( FE_INVALID ) |
| is raised. |
| .TP |
| Pole error: \fIx\fP is \-1 |
| .I errno |
| is set to |
| .BR ERANGE |
| (but see BUGS). |
| A divide-by-zero floating-point exception |
| .RB ( FE_DIVBYZERO ) |
| is raised. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .TS |
| allbox; |
| lbw27 lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR log1p (), |
| .BR log1pf (), |
| .BR log1pl () |
| T} Thread safety MT-Safe |
| .TE |
| .SH CONFORMING TO |
| C99, POSIX.1-2001, POSIX.1-2008. |
| .\" BSD |
| .SH BUGS |
| Before version 2.22, the glibc implementation did not set |
| .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792 |
| .I errno |
| to |
| .B EDOM |
| when a domain error occurred. |
| .PP |
| Before version 2.22, the glibc implementation did not set |
| .\" https://www.sourceware.org/bugzilla/show_bug.cgi?id=6792 |
| .I errno |
| to |
| .B ERANGE |
| when a range error occurred. |
| .SH SEE ALSO |
| .BR exp (3), |
| .BR expm1 (3), |
| .BR log (3) |