1 /*
2 * timespecops.h -- calculations on 'struct timespec' values
3 *
4 * Written by Juergen Perlinger (perlinger@ntp.org) for the NTP project.
5 * The contents of 'html/copyright.html' apply.
6 *
7 * Rationale
8 * ---------
9 *
10 * Doing basic arithmetic on a 'struct timespec' is not exceedingly
11 * hard, but it requires tedious and repetitive code to keep the result
12 * normalised. We consider a timespec normalised when the nanosecond
13 * fraction is in the interval [0 .. 10^9[ ; there are multiple value
14 * pairs of seconds and nanoseconds that denote the same time interval,
15 * but the normalised representation is unique. No two different
16 * intervals can have the same normalised representation.
17 *
18 * Another topic is the representation of negative time intervals.
19 * There's more than one way to this, since both the seconds and the
20 * nanoseconds of a timespec are signed values. IMHO, the easiest way is
21 * to use a complement representation where the nanoseconds are still
22 * normalised, no matter what the sign of the seconds value. This makes
23 * normalisation easier, since the sign of the integer part is
24 * irrelevant, and it removes several sign decision cases during the
25 * calculations.
26 *
27 * As long as no signed integer overflow can occur with the nanosecond
28 * part of the operands, all operations work as expected and produce a
29 * normalised result.
30 *
31 * The exception to this are functions fix a '_fast' suffix, which do no
32 * normalisation on input data and therefore expect the input data to be
33 * normalised.
34 *
35 * Input and output operands may overlap; all input is consumed before
36 * the output is written to.
37 */
38 #ifndef TIMESPECOPS_H
39 #define TIMESPECOPS_H
40
41 #include <sys/types.h>
42 #include <stdio.h>
43 #include <math.h>
44
45 #include "ntp.h"
46 #include "timetoa.h"
47
48
49 /* nanoseconds per second */
50 #define NANOSECONDS 1000000000
51
52 /* predicate: returns TRUE if the nanoseconds are in nominal range */
53 #define timespec_isnormal(x) \
54 ((x)->tv_nsec >= 0 && (x)->tv_nsec < NANOSECONDS)
55
56 /* predicate: returns TRUE if the nanoseconds are out-of-bounds */
57 #define timespec_isdenormal(x) (!timespec_isnormal(x))
58
59
60
61
62 /* make sure nanoseconds are in nominal range */
63 extern struct timespec normalize_tspec(struct timespec x);
64
65 /* x = a + b */
66 static inline struct timespec
add_tspec(struct timespec a,struct timespec b)67 add_tspec(
68 struct timespec a,
69 struct timespec b
70 )
71 {
72 struct timespec x;
73
74 x = a;
75 x.tv_sec += b.tv_sec;
76 x.tv_nsec += b.tv_nsec;
77
78 return normalize_tspec(x);
79 }
80
81 /* x = a + b, b is fraction only */
82 static inline struct timespec
add_tspec_ns(struct timespec a,long b)83 add_tspec_ns(
84 struct timespec a,
85 long b
86 )
87 {
88 struct timespec x;
89
90 x = a;
91 x.tv_nsec += b;
92
93 return normalize_tspec(x);
94 }
95
96 /* x = a - b */
97 static inline struct timespec
sub_tspec(struct timespec a,struct timespec b)98 sub_tspec(
99 struct timespec a,
100 struct timespec b
101 )
102 {
103 struct timespec x;
104
105 x = a;
106 x.tv_sec -= b.tv_sec;
107 x.tv_nsec -= b.tv_nsec;
108
109 return normalize_tspec(x);
110 }
111
112 /* x = a - b, b is fraction only */
113 static inline struct timespec
sub_tspec_ns(struct timespec a,long b)114 sub_tspec_ns(
115 struct timespec a,
116 long b
117 )
118 {
119 struct timespec x;
120
121 x = a;
122 x.tv_nsec -= b;
123
124 return normalize_tspec(x);
125 }
126
127 /* x = -a */
128 static inline struct timespec
neg_tspec(struct timespec a)129 neg_tspec(
130 struct timespec a
131 )
132 {
133 struct timespec x;
134
135 x.tv_sec = -a.tv_sec;
136 x.tv_nsec = -a.tv_nsec;
137
138 return normalize_tspec(x);
139 }
140
141 /* x = abs(a) */
142 struct timespec abs_tspec(struct timespec a);
143
144 /*
145 * compare previously-normalised a and b
146 * return 1 / 0 / -1 if a < / == / > b
147 */
148 extern int cmp_tspec(struct timespec a, struct timespec b);
149
150 /*
151 * compare possibly-denormal a and b
152 * return 1 / 0 / -1 if a < / == / > b
153 */
154 static inline int
cmp_tspec_denorm(struct timespec a,struct timespec b)155 cmp_tspec_denorm(
156 struct timespec a,
157 struct timespec b
158 )
159 {
160 return cmp_tspec(normalize_tspec(a), normalize_tspec(b));
161 }
162
163 /*
164 * test previously-normalised a
165 * return 1 / 0 / -1 if a < / == / > 0
166 */
167 extern int test_tspec(struct timespec a);
168
169 /*
170 * test possibly-denormal a
171 * return 1 / 0 / -1 if a < / == / > 0
172 */
173 static inline int
test_tspec_denorm(struct timespec a)174 test_tspec_denorm(
175 struct timespec a
176 )
177 {
178 return test_tspec(normalize_tspec(a));
179 }
180
181 /* return LIB buffer ptr to string rep */
182 static inline const char *
tspectoa(struct timespec x)183 tspectoa(
184 struct timespec x
185 )
186 {
187 return format_time_fraction(x.tv_sec, x.tv_nsec, 9);
188 }
189
190 /*
191 * convert to l_fp type, relative and absolute
192 */
193
194 /* convert from timespec duration to l_fp duration */
195 extern l_fp tspec_intv_to_lfp(struct timespec x);
196
197 /* x must be UN*X epoch, output will be in NTP epoch */
198 static inline l_fp
tspec_stamp_to_lfp(struct timespec x)199 tspec_stamp_to_lfp(
200 struct timespec x
201 )
202 {
203 l_fp y;
204
205 y = tspec_intv_to_lfp(x);
206 y.l_ui += JAN_1970;
207
208 return y;
209 }
210
211 /* convert from l_fp type, relative signed/unsigned and absolute */
212 extern struct timespec lfp_intv_to_tspec(l_fp x);
213 extern struct timespec lfp_uintv_to_tspec(l_fp x);
214
215 /*
216 * absolute (timestamp) conversion. Input is time in NTP epoch, output
217 * is in UN*X epoch. The NTP time stamp will be expanded around the
218 * pivot time *p or the current time, if p is NULL.
219 */
220 extern struct timespec lfp_stamp_to_tspec(l_fp x, const time_t *pivot);
221
222 #endif /* TIMESPECOPS_H */
223