format_tv.c

[詳解]

/*++
/* NAME
/*  format_tv 3
/* SUMMARY
/*  format time value with sane precision
/* SYNOPSIS
/*  #include <format_tv.h>
/*
/*  VSTRING *format_tv(buffer, sec, usec, sig_dig, max_dig)
/*  VSTRING *buffer;
/*  long    sec;
/*  long    usec;
/*  int sig_dig;
/*  int max_dig;
/* DESCRIPTION
/*  format_tv() formats the specified time as a floating-point
/*  number while suppressing irrelevant digits in the output.
/*  Large numbers are always rounded up to an integral number
/*  of seconds. Small numbers are produced with a limited number
/*  of significant digits, provided that the result does not
/*  exceed the limit on the total number of digits after the
/*  decimal point.  Trailing zeros are always omitted from the
/*  output.
/*
/*  Arguments:
/* .IP buffer
/*  The buffer to which the result is appended.
/* .IP sec
/*  The seconds portion of the time value.
/* .IP usec
/*  The microseconds portion of the time value.
/* .IP sig_dig
/*  The maximal number of significant digits when formatting
/*  small numbers. Leading nulls don't count as significant,
/*  and trailing nulls are not included in the output.  Specify
/*  a number in the range 1..6.
/* .IP max_dig
/*  The maximal number of all digits after the decimal point.
/*  Specify a number in the range 0..6.
/* LICENSE
/* .ad 
/* .fi
/*  The Secure Mailer license must be distributed with this
/*  software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*--*/

#include <sys_defs.h>

/* Utility library. */

#include <msg.h>
#include <format_tv.h>

/* Application-specific. */

#define MILLION 1000000

/* format_tv - print time with limited precision */

VSTRING *format_tv(VSTRING *buf, long sec, long usec,
                   int sig_dig, int max_dig)
{
    static int pow10[] = {1, 10, 100, 1000, 10000, 100000, 1000000};
    int     n;
    int     rem;
    int     wid;
    int     ures;

    /*
     * Sanity check.
     */
    if (max_dig < 0 || max_dig > 6)
    msg_panic("format_tv: bad maximum decimal count %d", max_dig);
    if (sec < 0 || usec < 0 || usec > MILLION)
    msg_panic("format_tv: bad time %lds %ldus", sec, usec);
    if (sig_dig < 1 || sig_dig > 6)
    msg_panic("format_tv: bad significant decimal count %d", sig_dig);
    ures = MILLION / pow10[max_dig];
    wid = pow10[sig_dig];

    /*
     * Adjust the resolution to suppress irrelevant digits.
     */
    if (ures < MILLION) {
    if (sec > 0) {
        for (n = 1; sec >= n && n <= wid / 10; n *= 10)
         /* void */ ;
        ures = (MILLION / wid) * n;
    } else {
        while (usec >= wid * ures)
        ures *= 10;
    }
    }

    /*
     * Round up the number if necessary. Leave thrash below the resolution.
     */
    if (ures > 1) {
    usec += ures / 2;
    if (usec >= MILLION) {
        sec += 1;
        usec -= MILLION;
    }
    }

    /*
     * Format the number. Truncate trailing null and thrash below resolution.
     */
    vstring_sprintf_append(buf, "%ld", sec);
    if (usec >= ures) {
    VSTRING_ADDCH(buf, '.');
    for (rem = usec, n = MILLION / 10; rem >= ures && n > 0; n /= 10) {
        VSTRING_ADDCH(buf, "0123456789"[rem / n]);
        rem %= n;
    }
    }
    VSTRING_TERMINATE(buf);
    return (buf);
}

#ifdef TEST

#include <stdio.h>
#include <stdlib.h>
#include <vstring_vstream.h>

int     main(int argc, char **argv)
{
    VSTRING *in = vstring_alloc(10);
    VSTRING *out = vstring_alloc(10);
    double  tval;
    int     sec;
    int     usec;
    int     sig_dig;
    int     max_dig;

    while (vstring_get_nonl(in, VSTREAM_IN) > 0) {
    vstream_printf(">> %s\n", vstring_str(in));
    if (vstring_str(in)[0] == 0 || vstring_str(in)[0] == '#')
        continue;
    if (sscanf(vstring_str(in), "%lf %d %d", &tval, &sig_dig, &max_dig) != 3)
        msg_fatal("bad input: %s", vstring_str(in));
    sec = (int) tval;           /* raw seconds */
    usec = (tval - sec) * MILLION;      /* raw microseconds */
    VSTRING_RESET(out);
    format_tv(out, sec, usec, sig_dig, max_dig);
    vstream_printf("%s\n", vstring_str(out));
    vstream_fflush(VSTREAM_OUT);
    }
    vstring_free(in);
    vstring_free(out);
    return (0);
}

#endif