LOGB(3) Linux Programmer's Manual LOGB(3)[top]NAMElogb, logbf,logbl- get exponent of a floating-point valueSYNOPSIS#include <math.h> double logb(double x); float logbf(float x); long double logbl(long double x); Link withFeature Test Macro Requirements for glibc (see feature_test_macros(7)): logb(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99 logbf(), logbl(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L; or cc -std=c99-lm.DESCRIPTIONThese functions extract the exponent from the internal floating-point representation of x and return it as a floating-point value. The inte‐ ger constant FLT_RADIX, defined in <float.h>, indicates the radix used for the system's floating-point representation. If FLT_RADIX is 2, logb(x) is equal to floor(log2(x)), except that it is probably faster. If x is subnormal, logb() returns the exponent x would have if it were normalized.RETURN VALUEOn success, these functions return the exponent of x. If x is a NaN, a NaN is returned. If x is zero, then a pole error occurs, and the functions return,-HUGE_VAL, or-HUGE_VALF, respectively. If x is negative infinity or positive infinity, then positive infinity is returned.-HUGE_VALLERRORSSee math_error(7) for information on how to determine whether an error has occurred when calling these functions. The following errors can occur: Pole error: x is 0 A divide-by-zero floating-point exception (FE_DIVBYZERO) is raised. These functions do not set errno.ATTRIBUTESMultithreading (see pthreads(7)) The logb(), logbf(), and logbl() functions are thread-safe.CONFORMING TOC99, POSIX.1-2001.SEE ALSOilogb(3), log(3)COLOPHONThis page is part of release 3.65 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. 2014-02-28 LOGB(3)

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