2004-11-03 13:51:07 +00:00
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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2007-06-20 22:33:04 +00:00
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.TH "ILOGB" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.\" ilogb
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2007-09-20 06:03:25 +00:00
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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2004-11-03 13:51:07 +00:00
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.SH NAME
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ilogb, ilogbf, ilogbl \- return an unbiased exponent
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.SH SYNOPSIS
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.LP
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\fB#include <math.h>
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.br
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.sp
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int ilogb(double\fP \fIx\fP\fB);
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.br
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int ilogbf(float\fP \fIx\fP\fB);
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.br
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int ilogbl(long double\fP \fIx\fP\fB);
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.br
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\fP
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.SH DESCRIPTION
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.LP
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These functions shall return the exponent part of their argument \fIx\fP.
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Formally, the return value is the integral part of
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log_r|x| as a signed integral value, for non-zero \fIx\fP, where \fIr\fP
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is the radix of the machine's floating-point
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arithmetic, which is the value of FLT_RADIX defined in \fI<float.h>\fP.
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.LP
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An application wishing to check for error situations should set \fIerrno\fP
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to zero and call
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\fIfeclearexcept\fP(FE_ALL_EXCEPT) before calling these functions.
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On return, if \fIerrno\fP is non-zero or
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\fIfetestexcept\fP(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW)
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is non-zero, an error has occurred.
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.SH RETURN VALUE
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.LP
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Upon successful completion, these functions shall return the exponent
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part of \fIx\fP as a signed integer value. They are
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equivalent to calling the corresponding \fIlogb\fP() function and
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casting the returned value
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to type \fBint\fP.
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.LP
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If \fIx\fP is 0, \ a domain error shall occur, and
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the value FP_ILOGB0 shall be returned.
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.LP
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If \fIx\fP is \(+-Inf, \ a domain error shall occur, and
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the value {INT_MAX} shall be returned.
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.LP
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If \fIx\fP is a NaN, \ a domain error shall occur, and
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the value FP_ILOGBNAN shall be returned.
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.LP
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If the correct value is greater than {INT_MAX}, {INT_MAX} shall be
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returned and a domain error shall occur.
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.LP
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If the correct value is less than {INT_MIN}, {INT_MIN} shall be returned
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and a domain error shall occur.
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.SH ERRORS
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.LP
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These functions shall fail if:
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.TP 7
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Domain\ Error
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The \fIx\fP argument is zero, NaN, or \(+-Inf, or the correct value
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is not representable as an integer.
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.LP
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If the integer expression (math_errhandling & MATH_ERRNO) is non-zero,
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then \fIerrno\fP shall be set to [EDOM]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the invalid floating-point exception shall be raised.
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.sp
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.LP
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\fIThe following sections are informative.\fP
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.SH EXAMPLES
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.LP
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None.
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.SH APPLICATION USAGE
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.LP
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On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling
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& MATH_ERREXCEPT) are independent of
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each other, but at least one of them must be non-zero.
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.SH RATIONALE
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.LP
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The errors come from taking the expected floating-point value and
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converting it to \fBint\fP, which is an invalid operation in
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IEEE\ Std\ 754-1985 (since overflow, infinity, and NaN are not representable
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in a type \fBint\fP), so should be a domain
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error.
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.LP
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There are no known implementations that overflow. For overflow to
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happen, {INT_MAX} must be less than
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LDBL_MAX_EXP*\fIlog2\fP(FLT_RADIX) or {INT_MIN} must be greater than
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LDBL_MIN_EXP*\fIlog2\fP(FLT_RADIX) if subnormals are not
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supported, or {INT_MIN} must be greater than (LDBL_MIN_EXP-LDBL_MANT_DIG)*\fIlog2\fP(FLT_RADIX)
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if subnormals are supported.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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2007-09-20 17:56:19 +00:00
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\fIfeclearexcept\fP(), \fIfetestexcept\fP(), \fIlogb\fP(), \fIscalb\fP(),
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the Base Definitions volume of
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2004-11-03 13:51:07 +00:00
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IEEE\ Std\ 1003.1-2001, Section 4.18, Treatment of Error Conditions
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for
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Mathematical Functions, \fI<float.h>\fP, \fI<math.h>\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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