logb - Online Linux Manual PageSection : 3
Updated : 2023-02-05
Source : Linux man-pages 6.03

NAMElogb, logbf, logbl − get exponent of a floating-point value

LIBRARYMath library (libm, −lm)

SYNOPSIS#include <math.h>double logb(double x); float logbf(float x); long double logbl(long double x);Feature Test Macro Requirements for glibc (see feature_test_macros(7)): logb(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCElogbf(), logbl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

DESCRIPTIONThese functions extract the exponent from the internal floating-point representation of x and return it as a floating-point value. The integer 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, HUGE_VALF, or HUGE_VALL, respectively. If x is negative infinity or positive infinity, then positive infinity is returned.

ERRORSSee 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.

ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7). InterfaceAttributeValue logb(), logbf(), logbl() Thread safetyMT-Safe

STANDARDSC99, POSIX.1-2001, POSIX.1-2008.

SEE ALSOilogb(3), log(3)
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