text: /* Copyright (C) 2005, 2008, 2009, 2011 Free Software Foundation, Inc.
     Contributed by Richard Henderson <rth@redhat.com>.
  
     This file is part of the GNU OpenMP Library (libgomp).
  
     Libgomp 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 3, or (at your option)
     any later version.
  
     Libgomp 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.
  
     Under Section 7 of GPL version 3, you are granted additional
     permissions described in the GCC Runtime Library Exception, version
     3.1, as published by the Free Software Foundation.
  
     You should have received a copy of the GNU General Public License and
     a copy of the GCC Runtime Library Exception along with this program;
     see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
     <http://www.gnu.org/licenses/>.  */
  
  /* This file contains routines for managing work-share iteration, both
     for loops and sections.  */
  
  #include "libgomp.h"
  #include <stdlib.h>
  
  
  /* This function implements the STATIC scheduling method.  The caller should
     iterate *pstart <= x < *pend.  Return zero if there are more iterations
     to perform; nonzero if not.  Return less than 0 if this thread had
     received the absolutely last iteration.  */
  
  int
  gomp_iter_static_next (long *pstart, long *pend)
  {
    struct gomp_thread *thr = gomp_thread ();
    struct gomp_team *team = thr->ts.team;
    struct gomp_work_share *ws = thr->ts.work_share;
    unsigned long nthreads = team ? team->nthreads : 1;
  
    if (thr->ts.static_trip == -1)
      return -1;
  
    /* Quick test for degenerate teams and orphaned constructs.  */
    if (nthreads == 1)
      {
        *pstart = ws->next;
        *pend = ws->end;
        thr->ts.static_trip = -1;
        return ws->next == ws->end;
      }
  
    /* We interpret chunk_size zero as "unspecified", which means that we
       should break up the iterations such that each thread makes only one
       trip through the outer loop.  */
    if (ws->chunk_size == 0)
      {
        unsigned long n, q, i, t;
        unsigned long s0, e0;
        long s, e;
  
        if (thr->ts.static_trip > 0)
  	return 1;
  
        /* Compute the total number of iterations.  */
        s = ws->incr + (ws->incr > 0 ? -1 : 1);
        n = (ws->end - ws->next + s) / ws->incr;
        i = thr->ts.team_id;
  
        /* Compute the "zero-based" start and end points.  That is, as
           if the loop began at zero and incremented by one.  */
        q = n / nthreads;
        t = n % nthreads;
        if (i < t)
  	{
  	  t = 0;
  	  q++;
  	}
        s0 = q * i + t;
        e0 = s0 + q;
  
        /* Notice when no iterations allocated for this thread.  */
        if (s0 >= e0)
  	{
  	  thr->ts.static_trip = 1;
  	  return 1;
  	}
  
        /* Transform these to the actual start and end numbers.  */
        s = (long)s0 * ws->incr + ws->next;
        e = (long)e0 * ws->incr + ws->next;
  
        *pstart = s;
        *pend = e;
        thr->ts.static_trip = (e0 == n ? -1 : 1);
        return 0;
      }
    else
      {
        unsigned long n, s0, e0, i, c;
        long s, e;
  
        /* Otherwise, each thread gets exactly chunk_size iterations
  	 (if available) each time through the loop.  */
  
        s = ws->incr + (ws->incr > 0 ? -1 : 1);
        n = (ws->end - ws->next + s) / ws->incr;
        i = thr->ts.team_id;
        c = ws->chunk_size;
  
        /* Initial guess is a C sized chunk positioned nthreads iterations
  	 in, offset by our thread number.  */
        s0 = (thr->ts.static_trip * nthreads + i) * c;
        e0 = s0 + c;
  
        /* Detect overflow.  */
        if (s0 >= n)
  	return 1;
        if (e0 > n)
  	e0 = n;
  
        /* Transform these to the actual start and end numbers.  */
        s = (long)s0 * ws->incr + ws->next;
        e = (long)e0 * ws->incr + ws->next;
  
        *pstart = s;
        *pend = e;
  
        if (e0 == n)
  	thr->ts.static_trip = -1;
        else
  	thr->ts.static_trip++;
        return 0;
      }
  }
  
  
  /* This function implements the DYNAMIC scheduling method.  Arguments are
     as for gomp_iter_static_next.  This function must be called with ws->lock
     held.  */
  
  bool
  gomp_iter_dynamic_next_locked (long *pstart, long *pend)
  {
    struct gomp_thread *thr = gomp_thread ();
    struct gomp_work_share *ws = thr->ts.work_share;
    long start, end, chunk, left;
  
    start = ws->next;
    if (start == ws->end)
      return false;
  
    chunk = ws->chunk_size;
    left = ws->end - start;
    if (ws->incr < 0)
      {
        if (chunk < left)
  	chunk = left;
      }
    else
      {
        if (chunk > left)
  	chunk = left;
      }
    end = start + chunk;
  
    ws->next = end;
    *pstart = start;
    *pend = end;
    return true;
  }
  
  
  #ifdef HAVE_SYNC_BUILTINS
  /* Similar, but doesn't require the lock held, and uses compare-and-swap
     instead.  Note that the only memory value that changes is ws->next.  */
  
  bool
  gomp_iter_dynamic_next (long *pstart, long *pend)
  {
    struct gomp_thread *thr = gomp_thread ();
    struct gomp_work_share *ws = thr->ts.work_share;
    long start, end, nend, chunk, incr;
  
    end = ws->end;
    incr = ws->incr;
    chunk = ws->chunk_size;
  
    if (__builtin_expect (ws->mode, 1))
      {
        long tmp = __sync_fetch_and_add (&ws->next, chunk);
        if (incr > 0)
  	{
  	  if (tmp >= end)
  	    return false;
  	  nend = tmp + chunk;
  	  if (nend > end)
  	    nend = end;
  	  *pstart = tmp;
  	  *pend = nend;
  	  return true;
  	}
        else
  	{
  	  if (tmp <= end)
  	    return false;
  	  nend = tmp + chunk;
  	  if (nend < end)
  	    nend = end;
  	  *pstart = tmp;
  	  *pend = nend;
  	  return true;
  	}
      }
  
    start = ws->next;
    while (1)
      {
        long left = end - start;
        long tmp;
  
        if (start == end)
  	return false;
  
        if (incr < 0)
  	{
  	  if (chunk < left)
  	    chunk = left;
  	}
        else
  	{
  	  if (chunk > left)
  	    chunk = left;
  	}
        nend = start + chunk;
  
        tmp = __sync_val_compare_and_swap (&ws->next, start, nend);
        if (__builtin_expect (tmp == start, 1))
  	break;
  
        start = tmp;
      }
  
    *pstart = start;
    *pend = nend;
    return true;
  }
  #endif /* HAVE_SYNC_BUILTINS */
  
  
  /* This function implements the GUIDED scheduling method.  Arguments are
     as for gomp_iter_static_next.  This function must be called with the
     work share lock held.  */
  
  bool
  gomp_iter_guided_next_locked (long *pstart, long *pend)
  {
    struct gomp_thread *thr = gomp_thread ();
    struct gomp_work_share *ws = thr->ts.work_share;
    struct gomp_team *team = thr->ts.team;
    unsigned long nthreads = team ? team->nthreads : 1;
    unsigned long n, q;
    long start, end;
  
    if (ws->next == ws->end)
      return false;
  
    start = ws->next;
    n = (ws->end - start) / ws->incr;
    q = (n + nthreads - 1) / nthreads;
  
    if (q < ws->chunk_size)
      q = ws->chunk_size;
    if (q <= n)
      end = start + q * ws->incr;
    else
      end = ws->end;
  
    ws->next = end;
    *pstart = start;
    *pend = end;
    return true;
  }
  
  #ifdef HAVE_SYNC_BUILTINS
  /* Similar, but doesn't require the lock held, and uses compare-and-swap
     instead.  Note that the only memory value that changes is ws->next.  */
  
  bool
  gomp_iter_guided_next (long *pstart, long *pend)
  {
    struct gomp_thread *thr = gomp_thread ();
    struct gomp_work_share *ws = thr->ts.work_share;
    struct gomp_team *team = thr->ts.team;
    unsigned long nthreads = team ? team->nthreads : 1;
    long start, end, nend, incr;
    unsigned long chunk_size;
  
    start = ws->next;
    end = ws->end;
    incr = ws->incr;
    chunk_size = ws->chunk_size;
  
    while (1)
      {
        unsigned long n, q;
        long tmp;
  
        if (start == end)
  	return false;
  
        n = (end - start) / incr;
        q = (n + nthreads - 1) / nthreads;
  
        if (q < chunk_size)
  	q = chunk_size;
        if (__builtin_expect (q <= n, 1))
  	nend = start + q * incr;
        else
  	nend = end;
  
        tmp = __sync_val_compare_and_swap (&ws->next, start, nend);
        if (__builtin_expect (tmp == start, 1))
  	break;
  
        start = tmp;
      }
  
    *pstart = start;
    *pend = nend;
    return true;
  }
  #endif /* HAVE_SYNC_BUILTINS */
  