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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 

.TH "ILOGB" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"

.\" ilogb 

.SH NAME

ilogb, ilogbf, ilogbl \- return an unbiased exponent

.SH SYNOPSIS

.LP

\fB#include <math.h>

.br

.sp

int ilogb(double\fP \fIx\fP\fB);

.br

int ilogbf(float\fP \fIx\fP\fB);

.br

int ilogbl(long double\fP \fIx\fP\fB);

.br

\fP

.SH DESCRIPTION

.LP

These functions shall return the exponent part of their argument \fIx\fP.

Formally, the return value is the integral part of

log_r|x| as a signed integral value, for non-zero \fIx\fP, where \fIr\fP

is the radix of the machine's floating-point

arithmetic, which is the value of FLT_RADIX defined in \fI<float.h>\fP.

.LP

An application wishing to check for error situations should set \fIerrno\fP

to zero and call

\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.

On return, if \fIerrno\fP is non-zero or

\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)

is non-zero, an error has occurred.

.SH RETURN VALUE

.LP

Upon successful completion, these functions shall return the exponent

part of \fIx\fP as a signed integer value. They are

equivalent to calling the corresponding \fIlogb\fP() function and

casting the returned value

to type \fBint\fP.

.LP

If \fIx\fP is 0,   \ a domain error shall occur, and 

the value FP_ILOGB0 shall be returned.

.LP

If \fIx\fP is \(+-Inf,   \ a domain error shall occur, and 

the value {INT_MAX} shall be returned.

.LP

If \fIx\fP is a NaN,   \ a domain error shall occur, and 

the value FP_ILOGBNAN shall be returned.

.LP

If the correct value is greater than {INT_MAX}, {INT_MAX} shall be

returned and a domain error shall occur.

.LP

If the correct value is less than {INT_MIN}, {INT_MIN} shall be returned

and a domain error shall occur. 

.SH ERRORS

.LP

These functions shall fail if:

.TP 7

Domain\ Error

The \fIx\fP argument is zero, NaN, or \(+-Inf, or the correct value

is not representable as an integer. 

.LP

If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,

then \fIerrno\fP 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.

.sp

.LP

\fIThe following sections are informative.\fP

.SH EXAMPLES

.LP

None.

.SH APPLICATION USAGE

.LP

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.

.SH RATIONALE

.LP

The errors come from taking the expected floating-point value and

converting it to \fBint\fP, which is an invalid operation in

IEEE\ Std\ 754-1985 (since overflow, infinity, and NaN are not representable

in a type \fBint\fP), so should be a domain

error.

.LP

There are no known implementations that overflow. For overflow to

happen, {INT_MAX} must be less than

LDBL_MAX_EXP*\fIlog2\fP(FLT_RADIX) or {INT_MIN} must be greater than

LDBL_MIN_EXP*\fIlog2\fP(FLT_RADIX) if subnormals are not

supported, or {INT_MIN} must be greater than (LDBL_MIN_EXP-LDBL_MANT_DIG)*\fIlog2\fP(FLT_RADIX)

if subnormals are supported.

.SH FUTURE DIRECTIONS

.LP

None.

.SH SEE ALSO

.LP

\fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIlogb\fP() , \fIscalb\fP()

, the Base Definitions volume of

IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment of Error Conditions

for

Mathematical Functions, \fI<float.h>\fP, \fI<math.h>\fP

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology

-- 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 .