1NEXTAFTER(3P) POSIX Programmer's Manual NEXTAFTER(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl
14 — next representable floating-point number
15
17 #include <math.h>
18 double nextafter(double x, double y);
20 float nextafterf(float x, float y);
21 long double nextafterl(long double x, long double y);
22 double nexttoward(double x, long double y);
23 float nexttowardf(float x, long double y);
24 long double nexttowardl(long double x, long double y);
25
27 The functionality described on this reference page is aligned with the
28 ISO C standard. Any conflict between the requirements described here
29 and the ISO C standard is unintentional. This volume of POSIX.1‐2008
30 defers to the ISO C standard.
31 The nextafter(), nextafterf(), and nextafterl() functions shall compute
33 the next representable floating-point value following x in the direc‐
34 tion of y. Thus, if y is less than x, nextafter() shall return the
35 largest representable floating-point number less than x. The
36 nextafter(), nextafterf(), and nextafterl() functions shall return y if
37 x equals y.
38 The nexttoward(), nexttowardf(), and nexttowardl() functions shall be
40 equivalent to the corresponding nextafter() functions, except that the
41 second parameter shall have type long double and the functions shall
42 return y converted to the type of the function if x equals y.
43 An application wishing to check for error situations should set errno
45 to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
46 functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
47 FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
48 occurred.
49
51 Upon successful completion, these functions shall return the next rep‐
52 resentable floating-point value following x in the direction of y.
53 If x==y, y (of the type x) shall be returned.
55 If x is finite and the correct function value would overflow, a range
57 error shall occur and ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (with the
58 same sign as x) shall be returned as appropriate for the return type of
59 the function.
60 If x or y is NaN, a NaN shall be returned.
62 If x!=y and the correct function value is subnormal, zero, or under‐
64 flows, a range error shall occur, and
65 the correct function value (if representable) or
66 0.0 shall be returned.
67
69 These functions shall fail if:
70 Range Error The correct value overflows.
72 If the integer expression (math_errhandling & MATH_ERRNO)
74 is non-zero, then errno shall be set to [ERANGE]. If the
75 integer expression (math_errhandling & MATH_ERREXCEPT) is
76 non-zero, then the overflow floating-point exception shall
77 be raised.
78 Range Error The correct value is subnormal or underflows.
80 If the integer expression (math_errhandling & MATH_ERRNO)
82 is non-zero, then errno shall be set to [ERANGE]. If the
83 integer expression (math_errhandling & MATH_ERREXCEPT) is
84 non-zero, then the underflow floating-point exception shall
85 be raised.
86 The following sections are informative.
88
90 None.
91
93 On error, the expressions (math_errhandling & MATH_ERRNO) and
94 (math_errhandling & MATH_ERREXCEPT) are independent of each other, but
95 at least one of them must be non-zero.
96 When <tgmath.h> is included, note that the return type of nextafter()
98 depends on the generic typing deduced from both arguments, while the
99 return type of nexttoward() depends only on the generic typing of the
100 first argument.
101
103 None.
104
106 None.
107
109 feclearexcept(), fetestexcept()
110 The Base Definitions volume of POSIX.1‐2008, Section 4.19, Treatment of
112 Error Conditions for Mathematical Functions, <math.h>, <tgmath.h>
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115 Portions of this text are reprinted and reproduced in electronic form
116 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
117 -- Portable Operating System Interface (POSIX), The Open Group Base
118 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
119 cal and Electronics Engineers, Inc and The Open Group. (This is
120 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
121 event of any discrepancy between this version and the original IEEE and
122 The Open Group Standard, the original IEEE and The Open Group Standard
123 is the referee document. The original Standard can be obtained online
124 at http://www.unix.org/online.html .
125 Any typographical or formatting errors that appear in this page are
127 most likely to have been introduced during the conversion of the source
128 files to man page format. To report such errors, see https://www.ker‐
129 nel.org/doc/man-pages/reporting_bugs.html .
130IEEE/The Open Group 2013 NEXTAFTER(3P)