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
12 nextafter, nextafterf, nextafterl, nexttoward, nexttowardf, nexttowardl
13 — next representable floating-point number
14
16 #include <math.h>
17 double nextafter(double x, double y);
19 float nextafterf(float x, float y);
20 long double nextafterl(long double x, long double y);
21 double nexttoward(double x, long double y);
22 float nexttowardf(float x, long double y);
23 long double nexttowardl(long double x, long double y);
24
26 The functionality described on this reference page is aligned with the
27 ISO C standard. Any conflict between the requirements described here
28 and the ISO C standard is unintentional. This volume of POSIX.1‐2017
29 defers to the ISO C standard.
30 The nextafter(), nextafterf(), and nextafterl() functions shall compute
32 the next representable floating-point value following x in the direc‐
33 tion of y. Thus, if y is less than x, nextafter() shall return the
34 largest representable floating-point number less than x. The
35 nextafter(), nextafterf(), and nextafterl() functions shall return y if
36 x equals y.
37 The nexttoward(), nexttowardf(), and nexttowardl() functions shall be
39 equivalent to the corresponding nextafter() functions, except that the
40 second parameter shall have type long double and the functions shall
41 return y converted to the type of the function if x equals y.
42 An application wishing to check for error situations should set errno
44 to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these
45 functions. On return, if errno is non-zero or fetestexcept(FE_INVALID |
46 FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has
47 occurred.
48
50 Upon successful completion, these functions shall return the next rep‐
51 resentable floating-point value following x in the direction of y.
52 If x==y, y (of the type x) shall be returned.
54 If x is finite and the correct function value would overflow, a range
56 error shall occur and ±HUGE_VAL, ±HUGE_VALF, and ±HUGE_VALL (with the
57 same sign as x) shall be returned as appropriate for the return type of
58 the function.
59 If x or y is NaN, a NaN shall be returned.
61 If x!=y and the correct function value is subnormal, zero, or under‐
63 flows, a range error shall occur, and
64 the correct function value (if representable) or
65 0.0 shall be returned.
66
68 These functions shall fail if:
69 Range Error The correct value overflows.
71 If the integer expression (math_errhandling & MATH_ERRNO)
73 is non-zero, then errno shall be set to [ERANGE]. If the
74 integer expression (math_errhandling & MATH_ERREXCEPT) is
75 non-zero, then the overflow floating-point exception shall
76 be raised.
77 Range Error The correct value is subnormal or underflows.
79 If the integer expression (math_errhandling & MATH_ERRNO)
81 is non-zero, then errno shall be set to [ERANGE]. If the
82 integer expression (math_errhandling & MATH_ERREXCEPT) is
83 non-zero, then the underflow floating-point exception shall
84 be raised.
85 The following sections are informative.
87
89 None.
90
92 On error, the expressions (math_errhandling & MATH_ERRNO) and
93 (math_errhandling & MATH_ERREXCEPT) are independent of each other, but
94 at least one of them must be non-zero.
95 When <tgmath.h> is included, note that the return type of nextafter()
97 depends on the generic typing deduced from both arguments, while the
98 return type of nexttoward() depends only on the generic typing of the
99 first argument.
100
102 None.
103
105 None.
106
108 feclearexcept(), fetestexcept()
109 The Base Definitions volume of POSIX.1‐2017, Section 4.20, Treatment of
111 Error Conditions for Mathematical Functions, <math.h>, <tgmath.h>
112
114 Portions of this text are reprinted and reproduced in electronic form
115 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
116 table Operating System Interface (POSIX), The Open Group Base Specifi‐
117 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
118 Electrical and Electronics Engineers, Inc and The Open Group. In the
119 event of any discrepancy between this version and the original IEEE and
120 The Open Group Standard, the original IEEE and The Open Group Standard
121 is the referee document. The original Standard can be obtained online
122 at http://www.opengroup.org/unix/online.html .
123 Any typographical or formatting errors that appear in this page are
125 most likely to have been introduced during the conversion of the source
126 files to man page format. To report such errors, see https://www.ker‐
127 nel.org/doc/man-pages/reporting_bugs.html .
128IEEE/The Open Group 2017 NEXTAFTER(3P)