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log2f(3m) [opensolaris man page]

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

NAME
log2, log2f, log2l - compute base 2 logarithm functions SYNOPSIS
c99 [ 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 5.11 12 Jul 2006 log2(3M)

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

NAME
log2, log2f, log2l - compute base 2 logarithm functions SYNOPSIS
#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, -HUGE_VALF, and -HUGE_VALL, respectively. For finite values of x that are less than 0, or if x is -Inf, 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. ERRORS
These functions shall fail if: Domain Error The finite value of x is less than zero, or x is -Inf. If 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. 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- ogy -- Portable 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)
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