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