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 */ 49const char * 50format_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