| .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
| .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk |
| .\" <mtk.manpages@gmail.com> |
| .\" |
| .\" %%%LICENSE_START(VERBATIM) |
| .\" Permission is granted to make and distribute verbatim copies of this |
| .\" manual provided the copyright notice and this permission notice are |
| .\" preserved on all copies. |
| .\" |
| .\" Permission is granted to copy and distribute modified versions of this |
| .\" manual under the conditions for verbatim copying, provided that the |
| .\" entire resulting derived work is distributed under the terms of a |
| .\" permission notice identical to this one. |
| .\" |
| .\" Since the Linux kernel and libraries are constantly changing, this |
| .\" manual page may be incorrect or out-of-date. The author(s) assume no |
| .\" responsibility for errors or omissions, or for damages resulting from |
| .\" the use of the information contained herein. The author(s) may not |
| .\" have taken the same level of care in the production of this manual, |
| .\" which is licensed free of charge, as they might when working |
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| .\" Formatted or processed versions of this manual, if unaccompanied by |
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| .\" %%%LICENSE_END |
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| .\" References consulted: |
| .\" Linux libc source code |
| .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) |
| .\" 386BSD man pages |
| .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu) |
| .\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no> |
| .\" Modified 2002-07-27 by Walter Harms |
| .\" (walter.harms@informatik.uni-oldenburg.de) |
| .\" |
| .TH LOG2 3 2017-09-15 "" "Linux Programmer's Manual" |
| .SH NAME |
| log2, log2f, log2l \- base-2 logarithmic function |
| .SH SYNOPSIS |
| .nf |
| .B #include <math.h> |
| .PP |
| .BI "double log2(double " x ); |
| .BI "float log2f(float " x ); |
| .BI "long double log2l(long double " x ); |
| .fi |
| .PP |
| 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 log2 (), |
| .BR log2f (), |
| .BR log2l (): |
| .RS 4 |
| _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L |
| .RE |
| .ad b |
| .SH DESCRIPTION |
| These functions return the base 2 logarithm of |
| .IR x . |
| .SH RETURN VALUE |
| On success, these functions return the base 2 logarithm of |
| .IR x . |
| .PP |
| For special cases, including where |
| .I x |
| is 0, 1, negative, infinity, or NaN, see |
| .BR log (3). |
| .SH ERRORS |
| See |
| .BR math_error (7) |
| for information on how to determine whether an error has occurred |
| when calling these functions. |
| .PP |
| For a discussion of the errors that can occur for these functions, see |
| .BR log (3). |
| .SH VERSIONS |
| These functions first appeared in glibc in version 2.1. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .TS |
| allbox; |
| lbw24 lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR log2 (), |
| .BR log2f (), |
| .BR log2l () |
| T} Thread safety MT-Safe |
| .TE |
| .SH CONFORMING TO |
| C99, POSIX.1-2001, POSIX.1-2008. |
| .PP |
| The variant returning |
| .I double |
| also conforms to |
| SVr4, 4.3BSD. |
| .SH SEE ALSO |
| .BR cbrt (3), |
| .BR clog2 (3), |
| .BR log (3), |
| .BR log10 (3), |
| .BR sqrt (3) |
