1 /* $NetBSD: timetoa.c,v 1.7 2020/05/25 20:47:24 christos Exp $ */
2
3 /*
4 * timetoa.c -- time_t related string formatting
5 *
6 * Written by Juergen Perlinger (perlinger@ntp.org) for the NTP project.
7 * The contents of 'html/copyright.html' apply.
8 *
9 * Printing a 'time_t' has a lot of portability pitfalls, due to it's
10 * opaque base type. The only requirement imposed by the standard is
11 * that it must be a numeric type. For all practical purposes it's a
12 * signed int, and 32 bits are common.
13 *
14 * Since the UN*X time epoch will cause a signed integer overflow for
15 * 32-bit signed int in the year 2038, implementations slowly move to
16 * 64bit base types for time_t, even in 32-bit environments.
17 *
18 * As the printf() family has no standardised type specifier for time_t,
19 * guessing the right output format specifier is a bit troublesome and
20 * best done with the help of the preprocessor and "config.h".
21 */
22
23 #include "config.h"
24
25 #include <math.h>
26 #include <stdio.h>
27
28 #include "timetoa.h"
29 #include "ntp_assert.h"
30 #include "lib_strbuf.h"
31
32 /*
33 * Formatting to string needs at max 40 bytes (even with 64 bit time_t),
34 * so we check LIB_BUFLENGTH is big enough for our purpose.
35 */
36 #if LIB_BUFLENGTH < 40
37 # include "GRONK: LIB_BUFLENGTH is not sufficient"
38 #endif
39
40 /*
41 * general fractional timestamp formatting
42 *
43 * Many pieces of ntpd require a machine with two's complement
44 * representation of signed integers, so we don't go through the whole
45 * rigamarole of creating fully portable code here. But we have to stay
46 * away from signed integer overflow, as this might cause trouble even
47 * with two's complement representation.
48 */
49 const char *
format_time_fraction(time_t secs,long frac,int prec)50 format_time_fraction(
51 time_t secs,
52 long frac,
53 int prec
54 )
55 {
56 char * cp;
57 u_int prec_u;
58 u_time secs_u;
59 u_int u;
60 long fraclimit;
61 int notneg; /* flag for non-negative value */
62 ldiv_t qr;
63
64 DEBUG_REQUIRE(prec != 0);
65
66 LIB_GETBUF(cp);
67 secs_u = (u_time)secs;
68
69 /* check if we need signed or unsigned mode */
70 notneg = (prec < 0);
71 prec_u = abs(prec);
72 /* fraclimit = (long)pow(10, prec_u); */
73 for (fraclimit = 10, u = 1; u < prec_u; u++) {
74 DEBUG_INSIST(fraclimit < fraclimit * 10);
75 fraclimit *= 10;
76 }
77
78 /*
79 * Since conversion to string uses lots of divisions anyway,
80 * there's no big extra penalty for normalisation. We do it for
81 * consistency.
82 */
83 if (frac < 0 || frac >= fraclimit) {
84 qr = ldiv(frac, fraclimit);
85 if (qr.rem < 0) {
86 qr.quot--;
87 qr.rem += fraclimit;
88 }
89 secs_u += (time_t)qr.quot;
90 frac = qr.rem;
91 }
92
93 /* Get the absolute value of the split representation time. */
94 notneg = notneg || ((time_t)secs_u >= 0);
95 if (!notneg) {
96 secs_u = ~secs_u;
97 if (0 == frac)
98 secs_u++;
99 else
100 frac = fraclimit - frac;
101 }
102
103 /* finally format the data and return the result */
104 snprintf(cp, LIB_BUFLENGTH, "%s%" UTIME_FORMAT ".%0*ld",
105 notneg? "" : "-", secs_u, prec_u, frac);
106
107 return cp;
108 }
109