# logbl(3) [posix 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)

## Check Out this Related Man Page

LOG1P(P)POSIX Programmer's Manual LOG1P(P)NAME

log1p, log1pf, log1pl - compute a natural logarithmSYNOPSIS

#include <math.h> double log1p(double x); float log1pf(float x); long double log1pl(long double x);DESCRIPTION

These functions shall compute log_e(1.0 + 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 natural logarithm of 1.0 + x. If x is, a pole error shall occur and log1p(), log1pf(), and log1pl() shall return-1,-HUGE_VAL, and-HUGE_VALF, respectively. For finite values of x that are less than-HUGE_VALL, or if x is-1, 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 +-0, or +Inf, x shall be returned. If x is subnormal, a range error may occur and x should be returned.-InfERRORS

These functions shall fail if: Domain Error The finite value of x is less than, or x is-1If 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-Inf.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. These functions may fail if: Range Error The value of x is subnormal. 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 underflow floating-point exception shall be raised. The following sections are informative.-1.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 LOG1P(P)