/* xnanosleep.c -- a more convenient interface to nanosleep
   Copyright (C) 2002 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,
   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* Mostly written (for sleep.c) by Paul Eggert.
   Factored out (creating this file) by Jim Meyering.  */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <stdio.h>
#include <assert.h>
#include <sys/types.h>
#include <time.h>

#define USE_CLOCK_GETTIME (defined CLOCK_REALTIME && HAVE_CLOCK_GETTIME)
#if ! USE_CLOCK_GETTIME
# include <sys/time.h>
#endif

#ifndef CHAR_BIT
# define CHAR_BIT 8
#endif

/* The extra casts work around common compiler bugs.  */
#define TYPE_SIGNED(t) (! ((t) 0 < (t) -1))
/* The outer cast is needed to work around a bug in Cray C 5.0.3.0.
   It is necessary at least when t == time_t.  */
#define TYPE_MINIMUM(t) ((t) (TYPE_SIGNED (t) \
			      ? ~ (t) 0 << (sizeof (t) * CHAR_BIT - 1) : (t) 0))
#define TYPE_MAXIMUM(t) ((t) (~ (t) 0 - TYPE_MINIMUM (t)))

#ifndef TIME_T_MAX
# define TIME_T_MAX TYPE_MAXIMUM (time_t)
#endif

#include "timespec.h"
#include "xalloc.h"
#include "xnanosleep.h"
#include "xstrtod.h"

#if HAVE_FENV_H
# include <fenv.h>
#endif

/* Tell the compiler that non-default rounding modes are used.  */
#if 199901 <= __STDC_VERSION__
 #pragma STDC FENV_ACCESS ON
#endif

static int initialized = 0;

/* Subtract the `struct timespec' values X and Y,
   storing the difference in DIFF.
   Return 1 if the difference is positive, otherwise 0.
   Derived from code in the GNU libc manual.  */

static int
timespec_subtract (struct timespec *diff,
		   const struct timespec *x, struct timespec *y)
{
  /* Perform the carry for the later subtraction by updating Y. */
  if (x->tv_nsec < y->tv_nsec)
    {
      int nsec = (y->tv_nsec - x->tv_nsec) / 1000000000 + 1;
      y->tv_nsec -= 1000000000 * nsec;
      y->tv_sec += nsec;
    }

  if (1000000000 < x->tv_nsec - y->tv_nsec)
    {
      int nsec = (y->tv_nsec - x->tv_nsec) / 1000000000;
      y->tv_nsec += 1000000000 * nsec;
      y->tv_sec -= nsec;
    }

  /* Compute the time remaining to wait.
     `tv_nsec' is certainly positive. */
  diff->tv_sec = x->tv_sec - y->tv_sec;
  diff->tv_nsec = x->tv_nsec - y->tv_nsec;

  /* Return 1 if result is positive. */
  return y->tv_sec < x->tv_sec;
}

struct timespec *
clock_get_realtime (struct timespec *ts)
{
  int fail;
#if USE_CLOCK_GETTIME
  fail = clock_gettime (CLOCK_REALTIME, ts);
#else
  struct timeval tv;
  fail = gettimeofday (&tv, NULL);
  if (!fail)
    {
      ts->tv_sec = tv.tv_sec;
      ts->tv_nsec = 1000 * tv.tv_usec;
    }
#endif

  if (fail)
    return NULL;

  return ts;
}

/* Sleep until the time (call it WAKE_UP_TIME) specified as
   SECONDS seconds after the time this function is called.
   SECONDS must be non-negative.  If SECONDS is so large that
   it is not representable as a `struct timespec', then use
   the maximum value for that interval.  */

int
xnanosleep (double seconds)
{
  int overflow;
  double ns;
  struct timespec ts_start;
  struct timespec ts_sleep;
  struct timespec ts_stop;

  assert (0 <= seconds);

#ifdef FE_UPWARD
  if (! initialized)
    {
      /* Always round up, since we must sleep for at least the specified
	 interval.  */
      /* FIXME: save and restore state, rather than just setting it?  */
      fesetround (FE_UPWARD);
    }
#endif

  if (clock_get_realtime (&ts_start) == NULL)
    return 1;

  /* Separate whole seconds from nanoseconds.
     Be careful to detect any overflow.  */
  ts_sleep.tv_sec = seconds;
  ns = 1e9 * (seconds - ts_sleep.tv_sec);
  overflow = ! (ts_sleep.tv_sec <= seconds && 0 <= ns && ns <= 1e9);
  ts_sleep.tv_nsec = ns;

  /* Round up to the next whole number, if necessary, so that we
     always sleep for at least the requested amount of time.  */
  ts_sleep.tv_nsec += (ts_sleep.tv_nsec < ns);

  /* Normalize the interval length.  nanosleep requires this.  */
  if (1000000000 <= ts_sleep.tv_nsec)
    {
      time_t t = ts_sleep.tv_sec + 1;

      /* Detect integer overflow.  */
      overflow |= (t < ts_sleep.tv_sec);

      ts_sleep.tv_sec = t;
      ts_sleep.tv_nsec -= 1000000000;
    }

  /* Compute the time until which we should sleep.  */
  ts_stop.tv_sec = ts_start.tv_sec + ts_sleep.tv_sec;
  ts_stop.tv_nsec = ts_start.tv_nsec + ts_sleep.tv_nsec;
  if (1000000000 <= ts_stop.tv_nsec)
    {
      ++ts_stop.tv_sec;
      ts_stop.tv_nsec -= 1000000000;
    }

  /* Detect integer overflow.  */
  overflow |= (ts_stop.tv_sec < ts_start.tv_sec
	       || (ts_stop.tv_sec == ts_start.tv_sec
		   && ts_stop.tv_nsec < ts_start.tv_nsec));

  if (overflow)
    {
      /* Fix ts_sleep and ts_stop, which may be garbage due to overflow.  */
      ts_sleep.tv_sec = ts_stop.tv_sec = TIME_T_MAX;
      ts_sleep.tv_nsec = ts_stop.tv_nsec = 999999999;
    }

  /* In case this process is suspended, then resumed, we'll know
     whether to resume sleeping.  */
  while (nanosleep (&ts_sleep, NULL) != 0
	 && timespec_subtract (&ts_sleep, &ts_stop,
			       clock_get_realtime (&ts_start)))
    {
      continue;
    }

  return 0;
}