1LOG10(3P)                  POSIX Programmer's Manual                 LOG10(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       log10, log10f, log10l — base 10 logarithm function
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SYNOPSIS

15       #include <math.h>
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17       double log10(double x);
18       float log10f(float x);
19       long double log10l(long double x);
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DESCRIPTION

22       The functionality described on this reference page is aligned with  the
23       ISO C  standard.  Any  conflict between the requirements described here
24       and the ISO C standard is unintentional. This  volume  of  POSIX.1‐2017
25       defers to the ISO C standard.
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27       These  functions  shall compute the base 10 logarithm of their argument
28       x, log10(x).
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30       An application wishing to check for error situations should  set  errno
31       to  zero  and  call  feclearexcept(FE_ALL_EXCEPT)  before calling these
32       functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
33       FE_DIVBYZERO  |  FE_OVERFLOW  | FE_UNDERFLOW) is non-zero, an error has
34       occurred.
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RETURN VALUE

37       Upon successful completion, these functions shall return  the  base  10
38       logarithm of x.
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40       If  x  is  ±0,  a  pole  error  shall  occur and log10(), log10f(), and
41       log10l() shall return -HUGE_VAL, -HUGE_VALF,  and  -HUGE_VALL,  respec‐
42       tively.
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44       For  finite values of x that are less than 0, or if x is -Inf, a domain
45       error shall occur, and either a NaN (if supported), or  an  implementa‐
46       tion-defined value shall be returned.
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48       If x is NaN, a NaN shall be returned.
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50       If x is 1, +0 shall be returned.
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52       If x is +Inf, +Inf shall be returned.
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ERRORS

55       These functions shall fail if:
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57       Domain Error
58                   The finite value of x is negative, or x is -Inf.
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60                   If  the  integer expression (math_errhandling & MATH_ERRNO)
61                   is non-zero, then errno shall be set  to  [EDOM].   If  the
62                   integer  expression  (math_errhandling & MATH_ERREXCEPT) is
63                   non-zero, then the invalid floating-point  exception  shall
64                   be raised.
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66       Pole Error  The value of x is zero.
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68                   If  the  integer expression (math_errhandling & MATH_ERRNO)
69                   is non-zero, then errno shall be set to [ERANGE].   If  the
70                   integer  expression  (math_errhandling & MATH_ERREXCEPT) is
71                   non-zero, then the divide-by-zero floating-point  exception
72                   shall be raised.
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74       The following sections are informative.
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EXAMPLES

77       None.
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APPLICATION USAGE

80       On   error,   the   expressions  (math_errhandling  &  MATH_ERRNO)  and
81       (math_errhandling & MATH_ERREXCEPT) are independent of each other,  but
82       at least one of them must be non-zero.
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RATIONALE

85       None.
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FUTURE DIRECTIONS

88       None.
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SEE ALSO

91       feclearexcept(), fetestexcept(), isnan(), log(), pow()
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93       The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of
94       Error Conditions for Mathematical Functions, <math.h>
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97       Portions of this text are reprinted and reproduced in  electronic  form
98       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
99       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
100       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
101       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
102       event of any discrepancy between this version and the original IEEE and
103       The Open Group Standard, the original IEEE and The Open Group  Standard
104       is  the  referee document. The original Standard can be obtained online
105       at http://www.opengroup.org/unix/online.html .
106
107       Any typographical or formatting errors that appear  in  this  page  are
108       most likely to have been introduced during the conversion of the source
109       files to man page format. To report such errors,  see  https://www.ker
110       nel.org/doc/man-pages/reporting_bugs.html .
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114IEEE/The Open Group                  2017                            LOG10(3P)
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