log2(3) [xfree86 man page]
LOG2(3) Linux Programmer's Manual LOG2(3) NAME
log2, log2f, log2l - base-2 logarithmic function SYNOPSIS
#include <math.h> double log2(double x); float log2f(float x); long double log2l(long double x); Link with -lm. Feature Test Macro Requirements for glibc (see feature_test_macros(7)): log2(), log2f(), log2l(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L DESCRIPTION
These functions return the base 2 logarithm of x. RETURN VALUE
On success, these functions return the base 2 logarithm of x. For special cases, including where x is 0, 1, negative, infinity, or NaN, see log(3). ERRORS
See math_error(7) for information on how to determine whether an error has occurred when calling these functions. For a discussion of the errors that can occur for these functions, see log(3). VERSIONS
These functions first appeared in glibc in version 2.1. ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). +-------------------------+---------------+---------+ |Interface | Attribute | Value | +-------------------------+---------------+---------+ |log2(), log2f(), log2l() | Thread safety | MT-Safe | +-------------------------+---------------+---------+ CONFORMING TO
C99, POSIX.1-2001, POSIX.1-2008. The variant returning double also conforms to SVr4, 4.3BSD. SEE ALSO
cbrt(3), clog2(3), log(3), log10(3), sqrt(3) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. 2017-09-15 LOG2(3)
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log2(3M) Mathematical Library Functions log2(3M) NAME
log2, log2f, log2l - compute base 2 logarithm functions SYNOPSIS
cc [ flag... ] file... -lm [ library... ] #include <math.h> double log2(double x); float log2f(float x); long double log2l(long double x); DESCRIPTION
These functions compute the base 2 logarithm of their argument x, log2(x). RETURN VALUES
Upon successful completion, these functions return the base 2 logarithm of x. If x is +-0, a pole error occurs and log2(), log2f(), and log2l() return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL, respectively. For finite values of x that are less than 0, or if x is -Inf a domain error occurs and a NaN is returned. If x is NaN, a NaN is returned. If x is 1, +0 is returned. If x is +Inf, x is returned. ERRORS
These functions will fail if: Domain Error The finite value of x is less than 0, or x is -Inf. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception is raised. Pole Error The value of x is 0. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the divide-by-zero floating-point exception is raised. USAGE
An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
feclearexcept(3M), fetestexcept(3M), log(3M), math.h(3HEAD), attributes(5), standards(5) SunOS 5.10 1 Sep 2002 log2(3M)