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LOG(3P) POSIX Programmer's Manual LOG(3P)PROLOGThis manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may dif- fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.NAMElog, logf, logl - natural logarithm functionSYNOPSIS#include<math.h>doublelog(doublex);floatlogf(floatx);longdoublelogl(longdoublex);DESCRIPTIONThese functions shall compute the natural logarithm of their argumentx, log_e(x). An application wishing to check for error situations should seterrnoto zero and callfeclearex-cept(FE_ALL_EXCEPT) before calling these functions. On return, iferrnois non-zero orfetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.RETURNVALUEUpon successful completion, these functions shall return the natural logarithm ofx. Ifxis ?0, a pole error shall occur andlog(),logf(), andlogl() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively. For finite values ofxthat are less than 0, or ifxis -Inf, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned. Ifxis NaN, a NaN shall be returned. Ifxis 1, +0 shall be returned. Ifxis +Inf,xshall be returned.ERRORSThese functions shall fail if: Domain Error The finite value ofxis negative, orxis -Inf. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, thenerrnoshall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point excep- tion shall be raised. Pole Error The value ofxis zero. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, thenerrnoshall be set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception shall be raised.Thefollowingsectionsareinformative.EXAMPLESNone.APPLICATIONUSAGEOn error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are indepen- dent of each other, but at least one of them must be non-zero.RATIONALENone.FUTUREDIRECTIONSNone.SEEALSOexp(),feclearexcept(),fetestexcept(),isnan(),log10(),log1p(), the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions,<math.h>COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan- dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica- tions Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan- dard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . IEEE/The Open Group 2003 LOG(3P)