107 lines
2.8 KiB
C
107 lines
2.8 KiB
C
/*
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* timetoa.c -- time_t related string formatting
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*
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* Written by Juergen Perlinger (perlinger@ntp.org) for the NTP project.
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* The contents of 'html/copyright.html' apply.
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*
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* Printing a 'time_t' has a lot of portability pitfalls, due to it's
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* opaque base type. The only requirement imposed by the standard is
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* that it must be a numeric type. For all practical purposes it's a
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* signed int, and 32 bits are common.
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*
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* Since the UN*X time epoch will cause a signed integer overflow for
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* 32-bit signed int in the year 2038, implementations slowly move to
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* 64bit base types for time_t, even in 32-bit environments.
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*
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* As the printf() family has no standardised type specifier for time_t,
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* guessing the right output format specifier is a bit troublesome and
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* best done with the help of the preprocessor and "config.h".
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*/
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#include "config.h"
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#include <math.h>
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#include <stdio.h>
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#include "timetoa.h"
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#include "ntp_assert.h"
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#include "lib_strbuf.h"
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/*
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* Formatting to string needs at max 40 bytes (even with 64 bit time_t),
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* so we check LIB_BUFLENGTH is big enough for our purpose.
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*/
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#if LIB_BUFLENGTH < 40
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# include "GRONK: LIB_BUFLENGTH is not sufficient"
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#endif
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/*
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* general fractional timestamp formatting
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*
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* Many pieces of ntpd require a machine with two's complement
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* representation of signed integers, so we don't go through the whole
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* rigamarole of creating fully portable code here. But we have to stay
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* away from signed integer overflow, as this might cause trouble even
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* with two's complement representation.
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*/
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const char *
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format_time_fraction(
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time_t secs,
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long frac,
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int prec
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)
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{
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char * cp;
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u_int prec_u;
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u_time secs_u;
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u_int u;
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long fraclimit;
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int notneg; /* flag for non-negative value */
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ldiv_t qr;
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DEBUG_REQUIRE(prec != 0);
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LIB_GETBUF(cp);
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secs_u = (u_time)secs;
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/* check if we need signed or unsigned mode */
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notneg = (prec < 0);
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prec_u = abs(prec);
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/* fraclimit = (long)pow(10, prec_u); */
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for (fraclimit = 10, u = 1; u < prec_u; u++) {
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DEBUG_INSIST(fraclimit < fraclimit * 10);
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fraclimit *= 10;
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}
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/*
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* Since conversion to string uses lots of divisions anyway,
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* there's no big extra penalty for normalisation. We do it for
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* consistency.
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*/
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if (frac < 0 || frac >= fraclimit) {
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qr = ldiv(frac, fraclimit);
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if (qr.rem < 0) {
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qr.quot--;
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qr.rem += fraclimit;
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}
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secs_u += (time_t)qr.quot;
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frac = qr.rem;
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}
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/* Get the absolute value of the split representation time. */
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notneg = notneg || ((time_t)secs_u >= 0);
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if (!notneg) {
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secs_u = ~secs_u;
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if (0 == frac)
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secs_u++;
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else
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frac = fraclimit - frac;
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}
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/* finally format the data and return the result */
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snprintf(cp, LIB_BUFLENGTH, "%s%" UTIME_FORMAT ".%0*ld",
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notneg? "" : "-", secs_u, prec_u, frac);
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return cp;
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}
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