mirror of https://github.com/mkerrisk/man-pages
182 lines
5.9 KiB
Plaintext
182 lines
5.9 KiB
Plaintext
.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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.TH "POW" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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.\" pow
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.SH NAME
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pow, powf, powl \- power function
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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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double pow(double\fP \fIx\fP\fB, double\fP \fIy\fP\fB);
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.br
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float powf(float\fP \fIx\fP\fB, float\fP \fIy\fP\fB);
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.br
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long double powl(long double\fP \fIx\fP\fB, long double\fP \fIy\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 compute the value of \fIx\fP raised to the power
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\fIy\fP, \fIx**y\fP. If
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\fIx\fP is negative, the application shall ensure that \fIy\fP is
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an integer value.
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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 value
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of \fIx\fP raised to the power \fIy\fP.
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.LP
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For finite values of \fIx\fP < 0, and finite non-integer values of
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\fIy\fP, a domain error shall occur and \ either a NaN
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(if representable), or an implementation-defined value shall be
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returned.
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.LP
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If the correct value would cause overflow, a range error shall occur
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and \fIpow\fP(), \fIpowf\fP(), and \fIpowl\fP() shall
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return \(+-HUGE_VAL, \(+-HUGE_VALF, and \(+-HUGE_VALL, respectively,
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with the same sign as the correct value of the
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function.
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.LP
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If the correct value would cause underflow, and is not representable,
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a range error may occur, and \ either 0.0 (if
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supported), or \ an implementation-defined value shall be
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returned.
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.LP
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If
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\fIx\fP or \fIy\fP is a NaN, a NaN shall be returned (unless specified
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elsewhere in this description).
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.LP
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For any value of \fIy\fP (including NaN), if \fIx\fP is +1, 1.0 shall
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be returned.
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.LP
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For any value of \fIx\fP (including NaN), if \fIy\fP is \(+-0, 1.0
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shall be returned.
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.LP
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For any odd integer value of \fIy\fP > 0, if \fIx\fP is \(+-0, \(+-0
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shall be returned.
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.LP
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For \fIy\fP > 0 and not an odd integer, if \fIx\fP is \(+-0, +0 shall
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be returned.
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.LP
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If \fIx\fP is -1, and \fIy\fP is \(+-Inf, 1.0 shall be returned.
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.LP
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For |\fIx\fP| < 1, if \fIy\fP is -Inf, +Inf shall be returned.
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.LP
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For |\fIx\fP| > 1, if \fIy\fP is -Inf, +0 shall be returned.
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.LP
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For |\fIx\fP| < 1, if \fIy\fP is +Inf, +0 shall be returned.
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.LP
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For |\fIx\fP| > 1, if \fIy\fP is +Inf, +Inf shall be returned.
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.LP
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For \fIy\fP an odd integer < 0, if \fIx\fP is -Inf, -0 shall be returned.
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.LP
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For \fIy\fP < 0 and not an odd integer, if \fIx\fP is -Inf, +0 shall
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be returned.
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.LP
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For \fIy\fP an odd integer > 0, if \fIx\fP is -Inf, -Inf shall be
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returned.
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.LP
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For \fIy\fP > 0 and not an odd integer, if \fIx\fP is -Inf, +Inf shall
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be returned.
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.LP
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For \fIy\fP < 0, if \fIx\fP is +Inf, +0 shall be returned.
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.LP
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For \fIy\fP > 0, if \fIx\fP is +Inf, +Inf shall be returned.
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.LP
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For \fIy\fP an odd integer < 0, if \fIx\fP is \(+-0, a pole error
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shall occur and \(+-HUGE_VAL, \(+-HUGE_VALF,
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and \(+-HUGE_VALL shall be returned for \fIpow\fP(), \fIpowf\fP(),
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and \fIpowl\fP(), respectively.
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.LP
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For \fIy\fP < 0 and not an odd integer, if \fIx\fP is \(+-0, a pole
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error shall occur and HUGE_VAL, HUGE_VALF, and
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HUGE_VALL shall be returned for \fIpow\fP(), \fIpowf\fP(), and \fIpowl\fP(),
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respectively.
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.LP
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If the correct value would cause underflow, and is representable,
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a range error may occur and the correct value shall be
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returned.
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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 value of \fIx\fP is negative and \fIy\fP is a finite non-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
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raised.
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.TP 7
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Pole\ Error
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The value of \fIx\fP is zero and \fIy\fP is negative.
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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 [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the divide-by-zero floating-point exception shall be
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raised.
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.TP 7
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Range\ Error
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The result overflows.
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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 [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the overflow floating-point exception shall be
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raised.
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.sp
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.LP
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These functions may fail if:
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.TP 7
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Range\ Error
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The result underflows.
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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 [ERANGE]. If the
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integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero,
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then the underflow floating-point exception shall be
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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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None.
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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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\fIexp\fP() , \fIfeclearexcept\fP() , \fIfetestexcept\fP() , \fIisnan\fP()
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, the Base Definitions volume of
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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<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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