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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21

DESCRIPTION

23       These functions shall compute the base 10 logarithm of  their  argument
24       x, log_10(x).
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26       An  application  wishing to check for error situations should set errno
27       to zero and  call  feclearexcept(FE_ALL_EXCEPT)  before  calling  these
28       functions.   On return, if errno is non-zero or fetestexcept(FE_INVALID
29       | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error  has
30       occurred.
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RETURN VALUE

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

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

73       None.
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APPLICATION USAGE

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

81       None.
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FUTURE DIRECTIONS

84       None.
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SEE ALSO

87       feclearexcept(), fetestexcept(), isnan(), log(), pow(), the Base  Defi‐
88       nitions  volume  of  IEEE Std 1003.1-2001,  Section  4.18, Treatment of
89       Error Conditions for Mathematical Functions, <math.h>
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92       Portions of this text are reprinted and reproduced in  electronic  form
93       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
94       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
95       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
96       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
97       event of any discrepancy between this version and the original IEEE and
98       The Open Group Standard, the original IEEE and The Open Group  Standard
99       is  the  referee document. The original Standard can be obtained online
100       at http://www.opengroup.org/unix/online.html .
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104IEEE/The Open Group                  2003                            LOG10(3P)
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