# log2f(3m) [opensolaris man page]

log2(3M) Mathematical Library Functions log2(3M)NAME

log2, log2f, log2l - compute base 2 logarithm functionsSYNOPSIS

c99 [ flag... ] file...[ library... ] #include <math.h> double log2(double x); float log2f(float x); long double log2l(long double x);-lmDESCRIPTION

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, and-HUGE_VALF, respectively. For finite values of x that are less than 0, or if x is-HUGE_VALLa 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.-InfERRORS

These functions will fail if: Domain Error The finite value of x is less than 0, or x isIf 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.-Inf.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 5.1112 Jul 2006 log2(3M)

## Check Out this Related Man Page

LOG2(P)POSIX Programmer's Manual LOG2(P)NAME

log2, log2f, log2l - compute base 2 logarithm functionsSYNOPSIS

#include <math.h> double log2(double x); float log2f(float x); long double log2l(long double x);DESCRIPTION

These functions shall compute the base 2 logarithm of their argument x, log_2(x). 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 VALUE

Upon successful completion, these functions shall return the base 2 logarithm of x. If x is +-0, a pole error shall occur and log2(), log2f(), and log2l() shall return,-HUGE_VAL, and-HUGE_VALF, respectively. For finite values of x that are less than 0, or if x is-HUGE_VALL, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned. If x is NaN, a NaN shall be returned. If x is 1, +0 shall be returned. If x is +Inf, x shall be returned.-InfERRORS

These functions shall fail if: Domain Error The finite value of x is less than zero, or x isIf the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised. Pole Error The value of x is zero. 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.-Inf.EXAMPLES

None.APPLICATION USAGE

On 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.RATIONALE

None.FUTURE DIRECTIONS

None.SEE ALSO

feclearexcept() , fetestexcept() , log() , the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogyPortable Operating System Interface (POSIX), The Open Group Base Specifications 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 Standard, 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 LOG2(P)