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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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log, logf, logl \- natural logarithm function
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double log(double\fP \fIx\fP\fB);
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float logf(float\fP \fIx\fP\fB);
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long double logl(long double\fP \fIx\fP\fB);
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These functions shall compute the natural logarithm of their argument
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An application wishing to check for error situations should set \fIerrno\fP
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\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
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On return, if \fIerrno\fP is non-zero or
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\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
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is non-zero, an error has occurred.
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Upon successful completion, these functions shall return the natural
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If \fIx\fP is \(+-0, a pole error shall occur and \fIlog\fP(), \fIlogf\fP(),
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and \fIlogl\fP() shall return -HUGE_VAL,
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-HUGE_VALF, and -HUGE_VALL, respectively.
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For finite values of \fIx\fP that are less than 0, \ or if \fIx\fP
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is -Inf, a domain error shall occur, and \ either a NaN (if supported),
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or \ an implementation-defined value shall be returned.
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\fIx\fP is NaN, a NaN shall be returned.
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If \fIx\fP is 1, +0 shall be returned.
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If \fIx\fP is +Inf, \fIx\fP shall be returned.
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These functions shall fail if:
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The finite value of \fIx\fP is negative, \ or \fIx\fP is -Inf.
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If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
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then \fIerrno\fP shall be set to [EDOM]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the invalid floating-point exception shall be
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The value of \fIx\fP is zero.
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If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
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then \fIerrno\fP shall be set to [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the divide-by-zero floating-point exception shall be
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\fIThe following sections are informative.\fP
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On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling
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& MATH_ERREXCEPT) are independent of
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each other, but at least one of them must be non-zero.
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\fIexp\fP() , \fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIisnan\fP()
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\fIlog1p\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001,
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Section 4.18, Treatment of Error Conditions for Mathematical Functions,
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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man3p/log.3p
