LOGB(3P) POSIX Programmer's Manual LOGB(3P)[top]PROLOGThis manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (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> double logb(double x); float logbf(float x); long double logbl(long double x);DESCRIPTIONThe functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2008 defers to the ISO C standard. These functions shall compute the exponent of x, which is the integral part of logr |x|, as a signed floating-point value, for non-zero x, where r is the radix of the machine's floating-point arithmetic, which is the value of FLT_RADIX defined in the <float.h> header. If x is subnormal it is treated as though it were normalized; thus for finite positive x: 1 <= x * FLT_RADIX−logb(x) < FLT_RADIX An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.RETURN VALUEUpon successful completion, these functions shall return the exponent of x. If x is ±0, logb(), logbf(), and logbl() shall return −HUGE_VAL, −HUGE_VALF, and −HUGE_VALL, respectively. On systems that support the IEC 60559 Floating-Point option, a pole error shall occur; otherwise, a pole error may occur. If x is NaN, a NaN shall be returned. If x is ±Inf, +Inf shall be returned.ERRORSThese functions shall fail if: Pole Error The value of x is ±0. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall 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. These functions may fail if: Pole Error The value of x is 0. If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall 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. The following sections are informative.EXAMPLESNone.APPLICATION USAGEOn error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.RATIONALENone.FUTURE DIRECTIONSNone.SEE ALSOfeclearexcept(), fetestexcept(), ilogb(), scalbln() The Base Definitions volume of POSIX.1‐2008, Section 4.19, 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, 2013 Edition, Standard for Information TechnologyPortable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐ cal and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html . Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.ker‐ nel.org/doc/man-pages/reporting_bugs.html .--IEEE/The Open Group 2013 LOGB(3P)

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