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+'\" t
+.\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
+.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
+.\"     <mtk.manpages@gmail.com>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" Inspired by a page by Walter Harms created 2002-08-10
+.\"
+.TH ilogb 3 2023-07-20 "Linux man-pages 6.05.01"
+.SH NAME
+ilogb, ilogbf, ilogbl \- get integer exponent of a floating-point value
+.SH LIBRARY
+Math library
+.RI ( libm ", " \-lm )
+.SH SYNOPSIS
+.nf
+.B #include <math.h>
+.PP
+.BI "int ilogb(double " x );
+.BI "int ilogbf(float " x );
+.BI "int ilogbl(long double " x );
+.fi
+.PP
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.PP
+.BR ilogb ():
+.nf
+    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
+        || _XOPEN_SOURCE >= 500
+.\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
+        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
+        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.fi
+.PP
+.BR ilogbf (),
+.BR ilogbl ():
+.nf
+    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
+        || /* Since glibc 2.19: */ _DEFAULT_SOURCE
+        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
+.fi
+.SH DESCRIPTION
+These functions return the exponent part of their argument
+as a signed integer.
+When no error occurs, these functions
+are equivalent to the corresponding
+.BR logb (3)
+functions, cast to
+.IR int .
+.SH RETURN VALUE
+On success, these functions return the exponent of
+.IR x ,
+as a signed integer.
+.PP
+If
+.I x
+is zero, then a domain error occurs, and the functions return
+.\" the POSIX.1 spec for logb() says logb() gives pole error for this
+.\" case, but for ilogb() it says domain error.
+.BR FP_ILOGB0 .
+.\" glibc: The numeric value is either `INT_MIN' or `-INT_MAX'.
+.PP
+If
+.I x
+is a NaN, then a domain error occurs, and the functions return
+.BR FP_ILOGBNAN .
+.\" glibc: The numeric value is either `INT_MIN' or `INT_MAX'.
+.\" On i386, FP_ILOGB0 and FP_ILOGBNAN have the same value.
+.PP
+If
+.I x
+is negative infinity or positive infinity, then
+a domain error occurs, and the functions return
+.BR INT_MAX .
+.\"
+.\" POSIX.1-2001 also says:
+.\" If the correct value is greater than {INT_MAX}, {INT_MAX}
+.\" shall be returned and a domain error shall occur.
+.\"
+.\" If the correct value is less than {INT_MIN}, {INT_MIN}
+.\" shall be returned and a domain error shall occur.
+.SH ERRORS
+See
+.BR math_error (7)
+for information on how to determine whether an error has occurred
+when calling these functions.
+.PP
+The following errors can occur:
+.TP
+Domain error: \fIx\fP is 0 or a NaN
+An invalid floating-point exception
+.RB ( FE_INVALID )
+is raised, and
+.I errno
+is set to
+.B EDOM
+(but see BUGS).
+.TP
+Domain error: \fIx\fP is an infinity
+An invalid floating-point exception
+.RB ( FE_INVALID )
+is raised, and
+.I errno
+is set to
+.B EDOM
+(but see BUGS).
+.SH ATTRIBUTES
+For an explanation of the terms used in this section, see
+.BR attributes (7).
+.TS
+allbox;
+lbx lb lb
+l l l.
+Interface	Attribute	Value
+T{
+.na
+.nh
+.BR ilogb (),
+.BR ilogbf (),
+.BR ilogbl ()
+T}	Thread safety	MT-Safe
+.TE
+.sp 1
+.SH STANDARDS
+C11, POSIX.1-2008.
+.SH HISTORY
+C99, POSIX.1-2001.
+.SH BUGS
+.\" Bug raised: https://www.sourceware.org/bugzilla/show_bug.cgi?id=6794
+Before glibc 2.16, the following bugs existed in the
+glibc implementation of these functions:
+.IP \[bu] 3
+The domain error case where
+.I x
+is 0 or a NaN did not cause
+.I errno
+to be set or (on some architectures) raise a floating-point exception.
+.IP \[bu]
+The domain error case where
+.I x
+is an infinity did not cause
+.I errno
+to be set or raise a floating-point exception.
+.SH SEE ALSO
+.BR log (3),
+.BR logb (3),
+.BR significand (3)