man3/log2.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
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  27 .\" References consulted:
  28 .\"     Linux libc source code
  29 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  30 .\"     386BSD man pages
  31 .\" Modified 1993-07-24 by Rik Faith (faith@cs.unc.edu)
  32 .\" Modified 1995-08-14 by Arnt Gulbrandsen <agulbra@troll.no>
  33 .\" Modified 2002-07-27 by Walter Harms
  34 .\"     (walter.harms@informatik.uni-oldenburg.de)
  35 .\"
  36 .TH LOG2 3  2016-03-15  "" "Linux Programmer's Manual"
  37 .SH NAME
  38 log2, log2f, log2l \- base-2 logarithmic function
  39 .SH SYNOPSIS
  40 .nf
  41 .B #include <math.h>
  42 .PP
  43 .BI "double log2(double " x );
  44 .br
  45 .BI "float log2f(float " x );
  46 .br
  47 .BI "long double log2l(long double " x );
  48 .fi
  49 .PP
  50 Link with \fI\-lm\fP.
  51 .PP
  52 .in -4n
  53 Feature Test Macro Requirements for glibc (see
  54 .BR feature_test_macros (7)):
  55 .in
  56 .PP
  57 .ad l
  58 .BR log2 (),
  59 .BR log2f (),
  60 .BR log2l ():
  61 .RS 4
  62 _ISOC99_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L
  63 .RE
  64 .ad b
  65 .SH DESCRIPTION
  66 These functions return the base 2 logarithm of
  67 .IR x .
  68 .SH RETURN VALUE
  69 On success, these functions return the base 2 logarithm of
  70 .IR x .
  71
  72 For special cases, including where
  73 .I x
  74 is 0, 1, negative, infinity, or NaN, see
  75 .BR log (3).
  76 .SH ERRORS
  77 See
  78 .BR math_error (7)
  79 for information on how to determine whether an error has occurred
  80 when calling these functions.
  81
  82 For a discussion of the errors that can occur for these functions, see
  83 .BR log (3).
  84 .SH VERSIONS
  85 These functions first appeared in glibc in version 2.1.
  86 .SH ATTRIBUTES
  87 For an explanation of the terms used in this section, see
  88 .BR attributes (7).
  89 .TS
  90 allbox;
  91 lbw24 lb lb
  92 l l l.
  93 Interface       Attribute       Value
  94 T{
  95 .BR log2 (),
  96 .BR log2f (),
  97 .BR log2l ()
  98 T}      Thread safety   MT-Safe
  99 .TE
 100 .SH CONFORMING TO
 101 C99, POSIX.1-2001, POSIX.1-2008.
 102
 103 The variant returning
 104 .I double
 105 also conforms to
 106 SVr4, 4.3BSD.
 107 .SH SEE ALSO
 108 .BR cbrt (3),
 109 .BR clog2 (3),
 110 .BR log (3),
 111 .BR log10 (3),
 112 .BR sqrt (3)