xref: /netbsd-src/external/bsd/ntp/dist/include/timetoa.h (revision cdfa2a7ef92791ba9db70a584a1d904730e6fb46)

/*	$NetBSD: timetoa.h,v 1.5 2020/05/25 20:47:20 christos Exp $	*/

/*
 * timetoa.h -- 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 some 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 values in the year 2038, implementations slowly
 * move to 64bit base types for time_t, even in 32-bit environments. In
 * such an environment sizeof(time_t) could be bigger than sizeof(long)
 * and the commonly used idiom of casting to long leads to truncation.
 *
 * 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".
 */
#ifndef TIMETOA_H
#define TIMETOA_H

#include "ntp_fp.h"
#include "ntp_stdlib.h"
#include "ntp_unixtime.h"

/*
 * Given the size of time_t, guess what can be used as an unsigned value
 * to hold a time_t and the printf() format specifcation.
 *
 * These should be used with the string constant concatenation feature
 * of the compiler like this:
 *
 * printf("a time stamp: %" TIME_FORMAT " and more\n", a_time_t_value);
 *
 * It's not exactly nice, but there's not much leeway once we want to
 * use the printf() family on time_t values.
 */

#if SIZEOF_TIME_T <= SIZEOF_INT

typedef unsigned int u_time;
#define TIME_FORMAT "d"
#define UTIME_FORMAT "u"

#elif SIZEOF_TIME_T <= SIZEOF_LONG

typedef unsigned long u_time;
#define TIME_FORMAT "ld"
#define UTIME_FORMAT "lu"

#elif defined(SIZEOF_LONG_LONG) && SIZEOF_TIME_T <= SIZEOF_LONG_LONG

typedef unsigned long long u_time;
#define TIME_FORMAT "lld"
#define UTIME_FORMAT "llu"

#else
#include "GRONK: what size has a time_t here?"
#endif

/*
 * general fractional time stamp formatting.
 *
 * secs - integral seconds of time stamp
 * frac - fractional units
 * prec - log10 of units per second (3=milliseconds, 6=microseconds,..)
 *	  or in other words: the count of decimal digits required.
 *	  If prec is < 0, abs(prec) is taken for the precision and secs
 *	  is treated as an unsigned value.
 *
 * The function will eventually normalise the fraction and adjust the
 * seconds accordingly.
 *
 * This function uses the string buffer library for the return value,
 * so do not keep the resulting pointers around.
 */
extern const char *
format_time_fraction(time_t secs, long frac, int prec);

#endif /* !defined(TIMETOA_H) */