# logb(3m) [sunos man page]

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

logb, logbf, logbl - radix-independent exponentSYNOPSIS

cc [ flag... ] file...[ library... ] #include <math.h> double logb(double x); float logbf(float x); long double logbl(long double x);-lmDESCRIPTION

These functions compute the exponent of x, which is the integral part of logr |x|, as a signed floating point value, for non-zero x, where r is the radix of the machine's floating-point arithmetic, which is the value of FLT_RADIX defined in the <float.h> header.RETURN VALUES

Upon successful completion, these functions return the exponent of x. If x is subnormal: o For SUSv3-conforming applications (see standards(5)), the exponent of x as if x were normalized is returned. o Otherwise,,-1022, and-126are returned for logb(), logbf(), and logbl(), respectively. If x is +-0, a pole error occurs and logb(), logbf(), and logbl() return-16382,-HUGE_VAL, and-HUGE_VALF, respectively. If x is NaN, a NaN is returned. If x is +-Inf, +Inf is returned.-HUGE_VALLERRORS

These functions will fail if: Pole Error The value of x is +-0. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the divide-by-zero floating-point exception is raised. The logb() function sets errno to EDOM if the value of x is 0.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. An application can also set errno to 0 before calling logb(). On return, if errno is non-zero, an error has occurred. The logbf() and logbl() functions do not set errno.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), ilogb(3M), math.h(3HEAD), matherr(3M), scalb(3M), attributes(5), standards(5)SunOS 5.101 Nov 2003 logb(3M)

## Check Out this Related Man Page

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

logb, logbf, logbl - radix-independent exponentSYNOPSIS

#include <math.h> double logb(double x); float logbf(float x); long double logbl(long double x);DESCRIPTION

These functions shall compute the exponent of x, which is the integral part of log_r |x|, as a signed floating-point value, for non-zero x, where r is the radix of the machine's floating-point arithmetic, which is the value of FLT_RADIX defined in the <float.h> header. If x is subnormal it is treated as though it were normalized; thus for finite positive x: 1 <= x * FLT_RADIX**-logb(x) < FLT_RADIX 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 exponent of x. If x is +-0, a pole error shall occur and logb(), logbf(), and logbl() shall return,-HUGE_VAL, and-HUGE_VALF, respectively. If x is NaN, a NaN shall be returned. If x is +-Inf, +Inf shall be returned.-HUGE_VALLERRORS

These functions shall fail if: Pole Error The value of x is +-0. 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() , ilogb() , scalb() , the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <float.h>, <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 LOGB(P)