/*
 * timespecops.h -- calculations on 'struct timespec' values
 *
 * Copyright Juergen Perlinger (perlinger@ntp.org)
 * Copyright the NTPsec project contributors
 * SPDX-License-Identifier: NTP

 *
 * Rationale
 * ---------
 *
 * Doing basic arithmetic on a 'struct timespec' is not exceedingly
 * hard, but it requires tedious and repetitive code to keep the result
 * normalised. We consider a timespec normalised when the nanosecond
 * fraction is in the interval [0 .. 10^9[ ; there are multiple value
 * pairs of seconds and nanoseconds that denote the same time interval,
 * but the normalised representation is unique. No two different
 * intervals can have the same normalised representation.
 *
 * Another topic is the representation of negative time intervals.
 * There's more than one way to this, since both the seconds and the
 * nanoseconds of a timespec are signed values. IMHO, the easiest way is
 * to use a complement representation where the nanoseconds are still
 * normalised, no matter what the sign of the seconds value. This makes
 * normalization easier, since the sign of the integer part is
 * irrelevant, and it removes several sign decision cases during the
 * calculations.
 *
 * As long as no signed integer overflow can occur with the nanosecond
 * part of the operands, all operations work as expected and produce a
 * normalised result.
 *
 * The exception to this are functions fix a '_fast' suffix, which do no
 * normalization on input data and therefore expect the input data to be
 * normalised.
 *
 * Input and output operands may overlap; all input is consumed before
 * the output is written to.
 *
 */
#include "config.h"

#include <stdio.h>
#include <math.h>

#include "timespecops.h"
#include "ntp.h"
#include "ntp_calendar.h"
#include "timetoa.h"

/* make sure nanoseconds are in nominal range */
struct timespec
normalize_tspec(
	struct timespec x
	)
{
#if NTP_SIZEOF_LONG > 4
	/*
	 * tv_nsec is of type 'long', and on a 64-bit machine using only
	 * loops becomes prohibitive once the upper 32 bits get
	 * involved. On the other hand, division by constant should be
	 * fast enough; so we do a division of the nanoseconds in that
	 * case.
	 */
	if (x.tv_nsec < 0 || x.tv_nsec >= NS_PER_S) {
		ldiv_t	z = ldiv( x.tv_nsec, NS_PER_S);
		if (z.rem < 0) {
			z.quot--;
			z.rem  += NS_PER_S;
		}
		x.tv_sec  += z.quot;
		x.tv_nsec  = z.rem;
	}
#else
	/* since 10**9 is close to 2**32, we don't divide but do a
	 * normalization in a loop; this takes 3 steps max, and should
	 * outperform a division even if the mul-by-inverse trick is
	 * employed. */
	if (x.tv_nsec < 0)
		do {
			x.tv_nsec += NS_PER_S;
			x.tv_sec--;
		} while (x.tv_nsec < 0);
	else if (x.tv_nsec >= NS_PER_S)
		do {
			x.tv_nsec -= NS_PER_S;
			x.tv_sec++;
		} while (x.tv_nsec >= NS_PER_S);
#endif

	return x;
}

/* convert a double to a rounded and normalized timespec */
struct timespec
d_to_tspec(
	double d
	)
{
	struct timespec	x;
	double s = floor(d);

	x.tv_sec  = (time_t) s;
	x.tv_nsec = (long) (((d - s) * NS_PER_S) + 0.5);
	return x;
}

/* convert a timespec to a double
 * will drop low bits if integer part is big
 */
double
tspec_to_d(
	struct timespec ts
	)
{
	return (ts.tv_sec + ts.tv_nsec*S_PER_NS);
}

/* x = a + b */
struct timespec
add_tspec(
	struct timespec	a,
	struct timespec	b
	)
{
	struct timespec	x;

	x = a;
	x.tv_sec += b.tv_sec;
	x.tv_nsec += b.tv_nsec;

	return normalize_tspec(x);
}

/* x = a + b, b is fraction only */
struct timespec
add_tspec_ns(
	struct timespec	a,
	long		b
	)
{
	struct timespec x;

	x = a;
	x.tv_nsec += b;

	return normalize_tspec(x);
}

/* x = a - b */
struct timespec
sub_tspec(
	struct timespec	a,
	struct timespec	b
	)
{
	struct timespec x;

	x = a;
	x.tv_sec -= b.tv_sec;
	x.tv_nsec -= b.tv_nsec;

	return normalize_tspec(x);
}

/* x = a - b, b is fraction only */
struct timespec
sub_tspec_ns(
	struct timespec	a,
	long		b
	)
{
	struct timespec	x;

	x = a;
	x.tv_nsec -= b;

	return normalize_tspec(x);
}

/* x = -a */
struct timespec
neg_tspec(
	struct timespec	a
	)
{
	struct timespec	x;

	x.tv_sec = -a.tv_sec;
	x.tv_nsec = -a.tv_nsec;

	return normalize_tspec(x);
}

/* x = abs(a) */
struct timespec
abs_tspec(
	struct timespec	a
	)
{
	struct timespec	c;

	c = normalize_tspec(a);
	if (c.tv_sec < 0) {
		if (c.tv_nsec != 0) {
			c.tv_sec = -c.tv_sec - 1;
			c.tv_nsec = NS_PER_S - c.tv_nsec;
		} else {
			c.tv_sec = -c.tv_sec;
		}
	}

	return c;
}

/*
 * compare previously-normalised a and b
 * return -1 / 0 / 1 if a < / == / > b
 */

int
cmp_tspec(
	struct timespec a,
	struct timespec b
	)
{
	int r;

	r = (a.tv_sec > b.tv_sec) - (a.tv_sec < b.tv_sec);
	if (0 == r)
		r = (a.tv_nsec > b.tv_nsec) -
		    (a.tv_nsec < b.tv_nsec);

	return r;
}

/*
 * compare possibly-denormal a and b
 * return -1 / 0 / 1 if a < / == / > b
 */
int
cmp_tspec_denorm(
	struct timespec	a,
	struct timespec	b
	)
{
	return cmp_tspec(normalize_tspec(a), normalize_tspec(b));
}

/*
 * test previously-normalised a
 * return -1 / 0 / 1 if a < / == / > 0
 */
int
test_tspec(
	struct timespec	a
	)
{
	int		r;

	r = (a.tv_sec > 0) - (a.tv_sec < 0);
	if (r == 0)
		r = (a.tv_nsec > 0);

	return r;
}

/*
 * test possibly-denormal a
 * return -1 / 0 / 1 if a < / == / > 0
 */
int
test_tspec_denorm(
	struct timespec	a
	)
{
	return test_tspec(normalize_tspec(a));
}

/*
 *  convert to l_fp type, relative and absolute
 */

/* convert from timespec duration to l_fp duration */
l_fp
tspec_intv_to_lfp(
	struct timespec	x
	)
{
	struct timespec	v = normalize_tspec(x);
	return lfpinit((int32_t)v.tv_sec, TVNTOF(v.tv_nsec));
}

/* x must be UN*X epoch, output will be in NTP epoch */
l_fp
tspec_stamp_to_lfp(
	struct timespec	x
	)
{
	l_fp		y;

	y = tspec_intv_to_lfp(x);
	bumplfpuint(y, JAN_1970);

	return y;
}

/* convert from l_fp type, relative signed/unsigned and absolute */
struct timespec
lfp_intv_to_tspec(
	l_fp		x
	)
{
	struct timespec out;
	l_fp		absx;
	int		neg;

	neg = L_ISNEG(x);
	absx = x;
	if (neg) {
		L_NEG(absx);
	}
	out.tv_nsec = FTOTVN(lfpfrac(absx));
	out.tv_sec = lfpsint(absx);
	if (neg) {
		out.tv_sec = -out.tv_sec;
		out.tv_nsec = -out.tv_nsec;
		out = normalize_tspec(out);
	}

	return out;
}

struct timespec
lfp_uintv_to_tspec(
	l_fp		x
	)
{
	struct timespec	out;

	out.tv_nsec = FTOTVN(lfpfrac(x));
	out.tv_sec  = lfpsint(x);

	return out;
}

/*
 * absolute (timestamp) conversion. Input is time in NTP epoch, output
 * is in UN*X epoch. The NTP time stamp will be expanded around the
 * pivot time p.
 */
struct timespec
lfp_stamp_to_tspec(
	l_fp		x,
	time_t	 	p
	)
{
	struct timespec	out;
	time64_t		sec;

	sec = ntpcal_ntp_to_time(lfpuint(x), p);
	out.tv_nsec = FTOTVN(lfpfrac(x));

	/* copying a time64_t to a time_t needs some care... */
#if NTP_SIZEOF_TIME_T <= 4
	out.tv_sec = (time_t)time64lo(sec);
#else
	out.tv_sec = (time_t)time64s(sec);
#endif

	return out;
}

struct timespec
tval_to_tspec(
    struct timeval x
    )
{
	struct timespec y;
	y.tv_sec = x.tv_sec;
	y.tv_nsec = x.tv_usec * 1000;
	return y;
}

/* end */
