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 * 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