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[thirdparty/man-pages.git] / man3 / logb.3

.\" Copyright 2004 Andries Brouwer <aeb@cwi.nl>.
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.\" Inspired by a page by Walter Harms created 2002-08-10
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.TH LOGB 3 2004-10-31 "" "Linux Programmer's Manual"
.SH NAME
logb, logbf, logbl \- get exponent of a floating point value
.SH SYNOPSIS
.B #include <math.h>
.sp
.BI "double logb(double " x );
.br
.BI "float logbf(float " x );
.br
.BI "long double logbl(long double " x );
.sp
Link with \-lm.
.SH DESCRIPTION
These functions extract the exponent of
.I x
and return it as a floating-point value.
If
.B FLT_RADIX
is two,
.BI logb( x )
is equal to
.BI floor(log2( x ))\fR,
except it's probably faster.
.LP
If
.I x
is de-normalized,
.BR logb ()
returns the exponent
.I x
would have if it were normalized.
.LP
If
.I x
is zero, \-HUGE_VAL (resp. \-HUGE_VALF, \-HUGE_VALL)
is returned, and a pole error occurs.
If
.I x
is infinite, plus infinity is returned.
If
.I x
is NaN, NaN is returned.
.\" .SH "RETURN VALUE"
.\" These functions return the exponent part of their argument.
.SH ERRORS
In order to check for errors, set
.I errno
to zero and call
.I feclearexcept(FE_ALL_EXCEPT)
before calling these functions.
On return, if
.I errno
is non-zero or
.I fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
is non-zero, an error has occurred.
.LP
If an error occurs and
.I "(math_errhandling & MATH_ERRNO)"
is non-zero, then
.I errno is set to
.BR ERANGE .
If an error occurs and
.I "(math_errhandling & MATH_ERREXCEPT)"
is non-zero, then the divide-by-zero floating-point exception is raised.
.LP
A pole error occurs when
.I x
is zero.
.SH HISTORY
The
.BR logb ()
function occurs in 4.3BSD.
.\" see IEEE.3 in the 4.3BSD manual
.SH "CONFORMING TO"
C99
.SH "SEE ALSO"
.BR log (3),
.BR ilogb (3)