mirror of https://github.com/mkerrisk/man-pages
117 lines
3.0 KiB
Groff
117 lines
3.0 KiB
Groff
.\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Inspired by a page by Walter Harms created 2002-08-10
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.\"
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.TH LOGB 3 2007-07-26 "" "Linux Programmer's Manual"
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.SH NAME
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logb, logbf, logbl \- get exponent of a floating point value
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.SH SYNOPSIS
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.B #include <math.h>
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.sp
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.BI "double logb(double " x );
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.br
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.BI "float logbf(float " x );
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.br
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.BI "long double logbl(long double " x );
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.sp
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Link with \fI\-lm\fP.
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.BR logb (),
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.BR logbf (),
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.BR logbl ():
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_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 || _ISOC99_SOURCE; or
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.I cc\ -std=c99
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.ad b
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.SH DESCRIPTION
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These functions extract the exponent of
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.I x
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and return it as a floating-point value.
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If
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.B FLT_RADIX
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is two,
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.BI logb( x )
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is equal to
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.BI floor(log2( x ))\fR,
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except that it is probably faster.
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.LP
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If
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.I x
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is de-normalized,
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.BR logb ()
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returns the exponent
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.I x
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would have if it were normalized.
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.LP
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If
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.I x
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is zero, \-\fBHUGE_VAL\fP (resp. \-\fBHUGE_VALF\fP, \-\fBHUGE_VALL\fP)
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is returned, and a pole error occurs.
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If
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.I x
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is infinite, plus infinity is returned.
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If
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.I x
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is NaN, NaN is returned.
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.\" .SH "RETURN VALUE"
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.\" These functions return the exponent part of their argument.
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.SH ERRORS
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In order to check for errors, set
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.I errno
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to zero and call
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.I feclearexcept(FE_ALL_EXCEPT)
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before calling these functions.
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On return, if
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.I errno
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is non-zero or
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.I fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
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is non-zero, an error has occurred.
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.LP
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If an error occurs and
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.I "(math_errhandling & MATH_ERRNO)"
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is non-zero, then
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.I errno is set to
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.BR ERANGE .
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If an error occurs and
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.I "(math_errhandling & MATH_ERREXCEPT)"
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is non-zero, then the divide-by-zero floating-point exception is raised.
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.LP
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A pole error occurs when
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.I x
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is zero.
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.\" .SH HISTORY
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.\" The
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.\" .BR logb ()
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.\" function occurs in 4.3BSD.
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.\" see IEEE.3 in the 4.3BSD manual
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.SH "CONFORMING TO"
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C99
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.SH "SEE ALSO"
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.BR log (3),
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.BR ilogb (3)
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