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