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LOGB(3P) POSIX Programmer's Manual LOGB(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.NAMElogb, logbf, logbl - radix-independent exponentSYNOPSIS#include<math.h>doublelogb(doublex);floatlogbf(floatx);longdoublelogbl(longdoublex);DESCRIPTIONThese functions shall compute the exponent ofx, which is the integral part of log_r|x|, as a signed floating- point value, for non-zerox, whereris the radix of the machine's floating-point arithmetic, which is the value of FLT_RADIX defined in the<float.h>header. Ifxis subnormal it is treated as though it were normalized; thus for finite positivex:1<=x*FLT_RADIX**-logb(x)<FLT_RADIXAn 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 exponent ofx. Ifxis ?0, a pole error shall occur andlogb(),logbf(), andlogbl() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively. Ifxis NaN, a NaN shall be returned. Ifxis ?Inf, +Inf shall be returned.ERRORSThese functions shall fail if: Pole Error The value ofxis ?0. 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.SEEALSOfeclearexcept(),fetestexcept(),ilogb(),scalb(), the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions,<float.h>,<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 LOGB(3P)