timetoa.c revision 1.2.4.2
1 1.2.4.2 yamt /* $NetBSD: timetoa.c,v 1.2.4.2 2014/05/22 15:50:08 yamt Exp $ */ 2 1.2.4.2 yamt 3 1.2.4.2 yamt /* 4 1.2.4.2 yamt * timetoa.c -- time_t related string formatting 5 1.2.4.2 yamt * 6 1.2.4.2 yamt * Written by Juergen Perlinger (perlinger (at) ntp.org) for the NTP project. 7 1.2.4.2 yamt * The contents of 'html/copyright.html' apply. 8 1.2.4.2 yamt * 9 1.2.4.2 yamt * Printing a 'time_t' has a lot of portability pitfalls, due to it's 10 1.2.4.2 yamt * opaque base type. The only requirement imposed by the standard is 11 1.2.4.2 yamt * that it must be a numeric type. For all practical purposes it's a 12 1.2.4.2 yamt * signed int, and 32 bits are common. 13 1.2.4.2 yamt * 14 1.2.4.2 yamt * Since the UN*X time epoch will cause a signed integer overflow for 15 1.2.4.2 yamt * 32-bit signed int in the year 2038, implementations slowly move to 16 1.2.4.2 yamt * 64bit base types for time_t, even in 32-bit environments. 17 1.2.4.2 yamt * 18 1.2.4.2 yamt * As the printf() family has no standardised type specifier for time_t, 19 1.2.4.2 yamt * guessing the right output format specifier is a bit troublesome and 20 1.2.4.2 yamt * best done with the help of the preprocessor and "config.h". 21 1.2.4.2 yamt */ 22 1.2.4.2 yamt 23 1.2.4.2 yamt #include "config.h" 24 1.2.4.2 yamt 25 1.2.4.2 yamt #include <math.h> 26 1.2.4.2 yamt #include <stdio.h> 27 1.2.4.2 yamt 28 1.2.4.2 yamt #include "timetoa.h" 29 1.2.4.2 yamt #include "ntp_assert.h" 30 1.2.4.2 yamt #include "lib_strbuf.h" 31 1.2.4.2 yamt 32 1.2.4.2 yamt /* 33 1.2.4.2 yamt * Formatting to string needs at max 40 bytes (even with 64 bit time_t), 34 1.2.4.2 yamt * so we check LIB_BUFLENGTH is big enough for our purpose. 35 1.2.4.2 yamt */ 36 1.2.4.2 yamt #if LIB_BUFLENGTH < 40 37 1.2.4.2 yamt # include "GRONK: LIB_BUFLENGTH is not sufficient" 38 1.2.4.2 yamt #endif 39 1.2.4.2 yamt 40 1.2.4.2 yamt /* 41 1.2.4.2 yamt * general fractional timestamp formatting 42 1.2.4.2 yamt * 43 1.2.4.2 yamt * Many pieces of ntpd require a machine with two's complement 44 1.2.4.2 yamt * representation of signed integers, so we don't go through the whole 45 1.2.4.2 yamt * rigamarole of creating fully portable code here. But we have to stay 46 1.2.4.2 yamt * away from signed integer overflow, as this might cause trouble even 47 1.2.4.2 yamt * with two's complement representation. 48 1.2.4.2 yamt */ 49 1.2.4.2 yamt const char * 50 1.2.4.2 yamt format_time_fraction( 51 1.2.4.2 yamt time_t secs, 52 1.2.4.2 yamt long frac, 53 1.2.4.2 yamt int prec 54 1.2.4.2 yamt ) 55 1.2.4.2 yamt { 56 1.2.4.2 yamt char * cp; 57 1.2.4.2 yamt u_int prec_u; 58 1.2.4.2 yamt u_time secs_u; 59 1.2.4.2 yamt u_int u; 60 1.2.4.2 yamt long fraclimit; 61 1.2.4.2 yamt int notneg; /* flag for non-negative value */ 62 1.2.4.2 yamt ldiv_t qr; 63 1.2.4.2 yamt 64 1.2.4.2 yamt DEBUG_REQUIRE(prec != 0); 65 1.2.4.2 yamt 66 1.2.4.2 yamt LIB_GETBUF(cp); 67 1.2.4.2 yamt secs_u = (u_time)secs; 68 1.2.4.2 yamt 69 1.2.4.2 yamt /* check if we need signed or unsigned mode */ 70 1.2.4.2 yamt notneg = (prec < 0); 71 1.2.4.2 yamt prec_u = abs(prec); 72 1.2.4.2 yamt /* fraclimit = (long)pow(10, prec_u); */ 73 1.2.4.2 yamt for (fraclimit = 10, u = 1; u < prec_u; u++) { 74 1.2.4.2 yamt DEBUG_INSIST(fraclimit < fraclimit * 10); 75 1.2.4.2 yamt fraclimit *= 10; 76 1.2.4.2 yamt } 77 1.2.4.2 yamt 78 1.2.4.2 yamt /* 79 1.2.4.2 yamt * Since conversion to string uses lots of divisions anyway, 80 1.2.4.2 yamt * there's no big extra penalty for normalisation. We do it for 81 1.2.4.2 yamt * consistency. 82 1.2.4.2 yamt */ 83 1.2.4.2 yamt if (frac < 0 || frac >= fraclimit) { 84 1.2.4.2 yamt qr = ldiv(frac, fraclimit); 85 1.2.4.2 yamt if (qr.rem < 0) { 86 1.2.4.2 yamt qr.quot--; 87 1.2.4.2 yamt qr.rem += fraclimit; 88 1.2.4.2 yamt } 89 1.2.4.2 yamt secs_u += (time_t)qr.quot; 90 1.2.4.2 yamt frac = qr.rem; 91 1.2.4.2 yamt } 92 1.2.4.2 yamt 93 1.2.4.2 yamt /* Get the absolute value of the split representation time. */ 94 1.2.4.2 yamt notneg = notneg || ((time_t)secs_u >= 0); 95 1.2.4.2 yamt if (!notneg) { 96 1.2.4.2 yamt secs_u = ~secs_u; 97 1.2.4.2 yamt if (0 == frac) 98 1.2.4.2 yamt secs_u++; 99 1.2.4.2 yamt else 100 1.2.4.2 yamt frac = fraclimit - frac; 101 1.2.4.2 yamt } 102 1.2.4.2 yamt 103 1.2.4.2 yamt /* finally format the data and return the result */ 104 1.2.4.2 yamt snprintf(cp, LIB_BUFLENGTH, "%s%" UTIME_FORMAT ".%0*ld", 105 1.2.4.2 yamt notneg? "" : "-", secs_u, prec_u, frac); 106 1.2.4.2 yamt 107 1.2.4.2 yamt return cp; 108 1.2.4.2 yamt } 109
Indexes created Mon Aug 17 00:26:26 UTC 2026