84 lines
2.6 KiB
C
84 lines
2.6 KiB
C
/*
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* timetoa.h -- 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 some portability pitfalls, due to it's opaque
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* base type. The only requirement imposed by the standard is that it
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* must be a numeric type. For all practical purposes it's a signed int,
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* 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 values in the year 2038, implementations slowly
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* move to 64bit base types for time_t, even in 32-bit environments. In
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* such an environment sizeof(time_t) could be bigger than sizeof(long)
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* and the commonly used idiom of casting to long leads to truncation.
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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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#ifndef TIMETOA_H
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#define TIMETOA_H
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#include "ntp_fp.h"
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#include "ntp_stdlib.h"
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#include "ntp_unixtime.h"
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/*
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* Given the size of time_t, guess what can be used as an unsigned value
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* to hold a time_t and the printf() format specifcation.
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*
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* These should be used with the string constant concatenation feature
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* of the compiler like this:
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*
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* printf("a time stamp: %" TIME_FORMAT " and more\n", a_time_t_value);
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*
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* It's not exactly nice, but there's not much leeway once we want to
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* use the printf() family on time_t values.
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*/
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#if SIZEOF_TIME_T <= SIZEOF_INT
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typedef unsigned int u_time;
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#define TIME_FORMAT "d"
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#define UTIME_FORMAT "u"
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#elif SIZEOF_TIME_T <= SIZEOF_LONG
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typedef unsigned long u_time;
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#define TIME_FORMAT "ld"
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#define UTIME_FORMAT "lu"
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#elif defined(SIZEOF_LONG_LONG) && SIZEOF_TIME_T <= SIZEOF_LONG_LONG
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typedef unsigned long long u_time;
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#define TIME_FORMAT "lld"
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#define UTIME_FORMAT "llu"
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#else
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#include "GRONK: what size has a time_t here?"
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#endif
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/*
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* general fractional time stamp formatting.
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*
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* secs - integral seconds of time stamp
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* frac - fractional units
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* prec - log10 of units per second (3=milliseconds, 6=microseconds,..)
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* or in other words: the count of decimal digits required.
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* If prec is < 0, abs(prec) is taken for the precision and secs
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* is treated as an unsigned value.
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*
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* The function will eventually normalise the fraction and adjust the
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* seconds accordingly.
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*
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* This function uses the string buffer library for the return value,
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* so do not keep the resulting pointers around.
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*/
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extern const char *
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format_time_fraction(time_t secs, long frac, int prec);
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#endif /* !defined(TIMETOA_H) */
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