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'\" et
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.TH NEXTAFTER "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
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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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.SH NAME
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nextafter,
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nextafterf,
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nextafterl,
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nexttoward,
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nexttowardf,
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nexttowardl
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\(em next representable floating-point number
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.SH SYNOPSIS
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.LP
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.nf
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#include <math.h>
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.P
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double nextafter(double \fIx\fP, double \fIy\fP);
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float nextafterf(float \fIx\fP, float \fIy\fP);
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long double nextafterl(long double \fIx\fP, long double \fIy\fP);
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double nexttoward(double \fIx\fP, long double \fIy\fP);
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float nexttowardf(float \fIx\fP, long double \fIy\fP);
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long double nexttowardl(long double \fIx\fP, long double \fIy\fP);
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.fi
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.SH DESCRIPTION
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The functionality described on this reference page is aligned with the
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ISO\ C standard. Any conflict between the requirements described here and the
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ISO\ C standard is unintentional. This volume of POSIX.1\(hy2008 defers to the ISO\ C standard.
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.P
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The
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\fInextafter\fR(),
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\fInextafterf\fR(),
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and
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\fInextafterl\fR()
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functions shall compute the next representable floating-point value
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following
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.IR x
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in the direction of
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.IR y .
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Thus, if
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.IR y
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is less than
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.IR x ,
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\fInextafter\fR()
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shall return the largest representable floating-point number less than
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.IR x .
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The
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\fInextafter\fR(),
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\fInextafterf\fR(),
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and
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\fInextafterl\fR()
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functions shall return
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.IR y
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if
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.IR x
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equals
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.IR y .
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.P
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The
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\fInexttoward\fR(),
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\fInexttowardf\fR(),
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and
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\fInexttowardl\fR()
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functions shall be equivalent to the corresponding
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\fInextafter\fR()
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functions, except that the second parameter shall have type
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.BR "long double"
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and the functions shall return
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.IR y
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converted to the type of the function if
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.IR x
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equals
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.IR y .
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.P
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An application wishing to check for error situations should set
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.IR errno
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to zero and call
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.IR feclearexcept (FE_ALL_EXCEPT)
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before calling these functions. On return, if
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.IR errno
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is non-zero or \fIfetestexcept\fR(FE_INVALID | FE_DIVBYZERO |
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FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
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.SH "RETURN VALUE"
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Upon successful completion, these functions shall return the next
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representable floating-point value following
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.IR x
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in the direction of
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.IR y .
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.P
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If
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.IR x ==\c
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.IR y ,
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.IR y
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(of the type
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.IR x )
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shall be returned.
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.P
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If
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.IR x
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is finite and the correct function value would overflow, a range error
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shall occur and \(+-HUGE_VAL, \(+-HUGE_VALF, and \(+-HUGE_VALL (with
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the same sign as
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.IR x )
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shall be returned as appropriate for the return type of the function.
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.P
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If
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.IR x
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or
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.IR y
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is NaN, a NaN shall be returned.
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.P
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If
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.IR x !=\c
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.IR y
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and the correct function value is subnormal, zero, or underflows,
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a range error shall occur, and
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.br
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the correct function value (if representable) or
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.br
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0.0 shall be returned.
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.SH ERRORS
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These functions shall fail if:
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.IP "Range\ Error" 12
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The correct value overflows.
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.RS 12
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.P
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If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
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non-zero, then
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.IR errno
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shall be set to
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.BR [ERANGE] .
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If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
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non-zero, then the overflow floating-point exception shall be raised.
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.RE
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.IP "Range\ Error" 12
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The correct value is subnormal or underflows.
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.RS 12
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.P
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If the integer expression (\fImath_errhandling\fR & MATH_ERRNO) is
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non-zero, then
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.IR errno
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shall be set to
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.BR [ERANGE] .
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If the integer expression (\fImath_errhandling\fR & MATH_ERREXCEPT) is
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non-zero, then the underflow floating-point exception shall be raised.
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.RE
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.LP
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.IR "The following sections are informative."
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.SH EXAMPLES
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None.
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.SH "APPLICATION USAGE"
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On error, the expressions (\fImath_errhandling\fR & MATH_ERRNO) and
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(\fImath_errhandling\fR & MATH_ERREXCEPT) are independent of each
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other, but at least one of them must be non-zero.
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.P
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When
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.IR <tgmath.h>
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is included, note that the return type of
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\fInextafter\fR()
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depends on the generic typing deduced from both arguments, while the
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return type of
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\fInexttoward\fR()
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depends only on the generic typing of the first argument.
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.SH RATIONALE
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None.
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.SH "FUTURE DIRECTIONS"
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None.
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.SH "SEE ALSO"
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.IR "\fIfeclearexcept\fR\^(\|)",
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.IR "\fIfetestexcept\fR\^(\|)"
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.P
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The Base Definitions volume of POSIX.1\(hy2008,
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.IR "Section 4.19" ", " "Treatment of Error Conditions for Mathematical Functions",
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.IR "\fB<math.h>\fP",
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.IR "\fB<tgmath.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, 2013 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 7, Copyright (C) 2013 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group.
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(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
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Any typographical or formatting errors that appear
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in this page are most likely
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to have been introduced during the conversion of the source files to
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man page format. To report such errors, see
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https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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