ilogb.3p (5519B)
- '\" et
- .TH ILOGB "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
- .\"
- .SH PROLOG
- This manual page is part of the POSIX Programmer's Manual.
- The Linux implementation of this interface may differ (consult
- the corresponding Linux manual page for details of Linux behavior),
- or the interface may not be implemented on Linux.
- .\"
- .EQ
- delim $$
- .EN
- .SH NAME
- ilogb,
- ilogbf,
- ilogbl
- \(em return an unbiased exponent
- .SH SYNOPSIS
- .LP
- .nf
- #include <math.h>
- .P
- int ilogb(double \fIx\fP);
- int ilogbf(float \fIx\fP);
- int ilogbl(long double \fIx\fP);
- .fi
- .SH DESCRIPTION
- The functionality described on this reference page is aligned with the
- ISO\ C standard. Any conflict between the requirements described here and the
- ISO\ C standard is unintentional. This volume of POSIX.1\(hy2017 defers to the ISO\ C standard.
- .P
- These functions shall return the exponent part of their argument
- .IR x .
- Formally, the return value is the integral part of $log sub{r}|x|$ as a
- signed integral value, for non-zero
- .IR x ,
- where
- .IR r
- is the radix of the machine's floating-point arithmetic, which is the
- value of FLT_RADIX defined in
- .IR <float.h> .
- .P
- An application wishing to check for error situations should set
- .IR errno
- to zero and call
- .IR feclearexcept (FE_ALL_EXCEPT)
- before calling these functions. On return, if
- .IR errno
- is non-zero or \fIfetestexcept\fR(FE_INVALID | FE_DIVBYZERO |
- FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
- .SH "RETURN VALUE"
- Upon successful completion, these functions shall return the exponent
- part of
- .IR x
- as a signed integer value. They are equivalent to calling the
- corresponding
- \fIlogb\fR()
- function and casting the returned value to type
- .BR int .
- .P
- If
- .IR x
- is 0, the value FP_ILOGB0 shall be returned.
- On XSI-conformant systems, a domain error shall occur;
- .br
- otherwise, a
- domain
- error may occur.
- .P
- If
- .IR x
- is \(+-Inf, the value
- {INT_MAX}
- shall be returned.
- On XSI-conformant systems, a domain error shall occur;
- .br
- otherwise, a
- domain
- error may occur.
- .P
- If
- .IR x
- is a NaN, the value FP_ILOGBNAN shall be returned.
- On XSI-conformant systems, a domain error shall occur;
- .br
- otherwise, a
- domain
- error may occur.
- .P
- If the correct value is greater than
- {INT_MAX},
- a domain error shall occur and
- an unspecified value shall be returned.
- On XSI-conformant systems, a domain error shall occur and
- {INT_MAX}
- shall be returned.
- .P
- If the correct value is less than
- {INT_MIN},
- a domain error shall occur and
- an unspecified value shall be returned.
- On XSI-conformant systems, a domain error shall occur and
- {INT_MIN}
- shall be returned.
- .SH ERRORS
- These functions shall fail if:
- .IP "Domain\ Error" 12
- The correct value is not representable as an integer.
- .RS 12
- .P
- The
- .IR x
- argument is zero, NaN, or \(+-Inf.
- .P
- If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
- non-zero, then
- .IR errno
- shall be set to
- .BR [EDOM] .
- If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
- non-zero, then the invalid floating-point exception shall be raised.
- .RE
- .P
- These functions may fail if:
- .IP "Domain\ Error" 12
- The
- .IR x
- argument is zero, NaN, or \(+-Inf.
- .RS 12
- .P
- If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
- non-zero, then
- .IR errno
- shall be set to
- .BR [EDOM] .
- If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
- non-zero, then the invalid floating-point exception shall be raised.
- .RE
- .LP
- .IR "The following sections are informative."
- .SH EXAMPLES
- None.
- .SH "APPLICATION USAGE"
- On error, the expressions (\fImath_errhandling\fR & MATH_ERRNO) and
- (\fImath_errhandling\fR & MATH_ERREXCEPT) are independent of each
- other, but at least one of them must be non-zero.
- .SH RATIONALE
- The errors come from taking the expected floating-point value and
- converting it to
- .BR int ,
- which is an invalid operation in IEEE\ Std\ 754\(hy1985 (since overflow, infinity, and
- NaN are not representable in a type
- .BR int ),
- so should be a domain error.
- .P
- 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"
- None.
- .SH "SEE ALSO"
- .IR "\fIfeclearexcept\fR\^(\|)",
- .IR "\fIfetestexcept\fR\^(\|)",
- .IR "\fIlogb\fR\^(\|)",
- .IR "\fIscalbln\fR\^(\|)"
- .P
- The Base Definitions volume of POSIX.1\(hy2017,
- .IR "Section 4.20" ", " "Treatment of Error Conditions for Mathematical Functions",
- .IR "\fB<float.h>\fP",
- .IR "\fB<math.h>\fP"
- .\"
- .SH COPYRIGHT
- Portions of this text are reprinted and reproduced in electronic form
- from IEEE Std 1003.1-2017, Standard for Information Technology
- -- Portable Operating System Interface (POSIX), The Open Group Base
- Specifications Issue 7, 2018 Edition,
- Copyright (C) 2018 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 .
- .PP
- Any typographical or formatting errors that appear
- in this page are most likely
- to have been introduced during the conversion of the source files to
- man page format. To report such errors, see
- https://www.kernel.org/doc/man-pages/reporting_bugs.html .