man3/log2.3

   1 '\" t
   2 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   3 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   4 .\"     <mtk.manpages@gmail.com>
   5 .\"
   6 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   7 .\"
   8 .\" References consulted:
   9 .\"     Linux libc source code
  10 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  11 .\"     386BSD man pages
  12 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  13 .\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no>
  14 .\" Modified 2002-07-27 by Walter Harms
  15 .\"     (walter.harms@informatik.uni-oldenburg.de)
  16 .\"
  17 .TH log2 3 (date) "Linux man-pages (unreleased)"
  18 .SH NAME
  19 log2, log2f, log2l \- base-2 logarithmic function
  20 .SH LIBRARY
  21 Math library
  22 .RI ( libm ", " \-lm )
  23 .SH SYNOPSIS
  24 .nf
  25 .B #include <math.h>
  26 .P
  27 .BI "double log2(double " x );
  28 .BI "float log2f(float " x );
  29 .BI "long double log2l(long double " x );
  30 .fi
  31 .P
  32 .RS -4
  33 Feature Test Macro Requirements for glibc (see
  34 .BR feature_test_macros (7)):
  35 .RE
  36 .P
  37 .BR log2 (),
  38 .BR log2f (),
  39 .BR log2l ():
  40 .nf
  41     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  42 .fi
  43 .SH DESCRIPTION
  44 These functions return the base-2 logarithm of
  45 .IR x .
  46 .SH RETURN VALUE
  47 On success, these functions return the base-2 logarithm of
  48 .IR x .
  49 .P
  50 For special cases, including where
  51 .I x
  52 is 0, 1, negative, infinity, or NaN, see
  53 .BR log (3).
  54 .SH ERRORS
  55 See
  56 .BR math_error (7)
  57 for information on how to determine whether an error has occurred
  58 when calling these functions.
  59 .P
  60 For a discussion of the errors that can occur for these functions, see
  61 .BR log (3).
  62 .SH ATTRIBUTES
  63 For an explanation of the terms used in this section, see
  64 .BR attributes (7).
  65 .TS
  66 allbox;
  67 lbx lb lb
  68 l l l.
  69 Interface       Attribute       Value
  70 T{
  71 .na
  72 .nh
  73 .BR log2 (),
  74 .BR log2f (),
  75 .BR log2l ()
  76 T}      Thread safety   MT-Safe
  77 .TE
  78 .SH STANDARDS
  79 C11, POSIX.1-2008.
  80 .SH HISTORY
  81 glibc 2.1.
  82 C99, POSIX.1-2001.
  83 .P
  84 The variant returning
  85 .I double
  86 also conforms to
  87 SVr4, 4.3BSD.
  88 .SH SEE ALSO
  89 .BR cbrt (3),
  90 .BR clog2 (3),
  91 .BR log (3),
  92 .BR log10 (3),
  93 .BR sqrt (3)