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+// This may look like C code, but it is really -*- C++ -*-
+
+/*
+Copyright (C) 1991 Free Software Foundation
+
+This file is part of the GNU C++ Library. This library is free
+software; you can redistribute it and/or modify it under the terms of
+the GNU Library General Public License as published by the Free
+Software Foundation; either version 2 of the License, or (at your
+option) any later version. This library 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 Library General Public License for more details.
+You should have received a copy of the GNU Library General Public
+License along with this library; if not, write to the Free Software
+Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+*/
+
+/*
+ * Bags implemented via William Pugh SkipList algorithms.
+ * CACM, June 1990, p 668-676.
+ *
+ */
+
+#include <stream.h>
+#include <time.h>
+#include "<T>.SkipBag.h"
+
+MLCG* <T>SkipBag::gen = 0;
+int <T>SkipBaginit::count = 0;
+
+static int countbits(long bits)
+{
+ int n = 0;
+ while(bits>>=1L) n++;
+ return n;
+}
+
+<T>SkipBag::<T>SkipBag(long size)
+: level(0),
+ header(new <T>SkipBagNode (countbits(size)+1)),
+ max_levels (countbits(size)+1),
+ random_bits(gen->asLong()),
+ randoms_left(BITS_IN_RANDOM / 2)
+{
+ <T>SkipBagNodePtr *buffer_start = header->forward;
+ <T>SkipBagNodePtr *trav = &header->forward[max_levels];
+
+ count = 0;
+ while (trav > buffer_start)
+ *--trav = (<T>SkipBagNodePtr) header;
+}
+
+<T>SkipBag::<T>SkipBag(<T>SkipBag& b)
+: level (0),
+ header (new <T>SkipBagNode (b.max_levels)),
+ max_levels (b.max_levels),
+ random_bits (gen->asLong()),
+ randoms_left (BITS_IN_RANDOM / 2)
+{
+ <T>SkipBagNodePtr *buffer_start = header->forward;
+ <T>SkipBagNodePtr *trav = &header->forward[max_levels];
+
+ count = 0;
+
+ while (trav > buffer_start)
+ *--trav = (<T>SkipBagNodePtr)header;
+
+ for (<T>SkipBagNodePtr t = b.leftmost(); t; t = b.succ(t))
+ add(t->item);
+}
+
+Pix <T>SkipBag::add (<T&> item)
+{
+ <T>SkipBagNodePtr *update = new <T>SkipBagNodePtr[max_levels+1];
+ <T>SkipBagNodePtr curr = (<T>SkipBagNodePtr) this->header;
+ int l = level;
+ <T>SkipBagNodePtr temp;
+
+ do
+ {
+ while ((temp = curr->forward[l])!=header &&
+ <T>CMP(temp->item, item) < 0)
+ curr = temp;
+ update[l] = curr;
+ }
+ while (--l >= 0);
+
+ if ((l = random_level ()) > level)
+ {
+ l = ++level;
+ update[l] = (<T>SkipBagNodePtr)header;
+ };
+
+ temp = new <T>RealSkipBagNode (item, l);
+ <T>SkipBagNodePtr *temp_forward = temp->forward;
+
+ do
+ {
+ <T>SkipBagNodePtr *curr_forward = update[l]->forward;
+
+ temp_forward[l] = curr_forward[l];
+ curr_forward[l] = temp;
+ }
+ while (--l >= 0);
+
+ count++;
+ delete update;
+ return Pix(temp);
+}
+
+void <T>SkipBag::del(<T&> key)
+{
+
+ int l = level;
+ int curr_level = level;
+ <T>SkipBagNodePtr *update = new <T>SkipBagNodePtr[max_levels+1];
+ <T>SkipBagNodePtr curr = (<T>SkipBagNodePtr)header;
+ <T>SkipBagNodePtr temp;
+
+ do
+ {
+ while ((temp = curr->forward[l])!=header
+ && <T>CMP(temp->item,key) < 0)
+ curr = temp;
+ update[l] = curr;
+ }
+ while (--l >= 0);
+
+ if (<T>CMP(temp->item,key)==0)
+ {
+ <T>SkipBagNodePtr *temp_forward = temp->forward;
+
+ for (l = 0;
+ l <= curr_level && (curr = update[l])->forward[l] == temp;
+ l++)
+ curr->forward[l] = temp_forward[l];
+
+ delete temp;
+
+ <T>SkipBagNodePtr *forward = header->forward;
+
+ while (forward[curr_level]==header && curr_level > 0)
+ curr_level--;
+
+ level = curr_level;
+ count--;
+ delete update;
+ return;
+ }
+}
+
+<T>SkipBagNodePtr <T>SkipBag::rightmost()
+{
+ <T>SkipBagNodePtr temp;
+ <T>SkipBagNode* curr = header;
+ int l = level;
+
+ do
+ while ((temp = curr->forward[l])!=header)
+ curr = temp;
+ while (--l >= 0);
+
+ return temp==header ? 0 : temp;
+}
+
+<T>SkipBagNodePtr <T>SkipBag::pred(<T>SkipBagNodePtr t)
+{
+ <T>SkipBagNodePtr temp, curr = (<T>SkipBagNodePtr) header;
+ int l = level;
+
+ do
+ while ((temp = curr->forward[l])!=t)
+ curr = temp;
+ while (--l >= 0);
+
+ return curr == header ? 0 : curr;
+}
+
+void <T>SkipBag::_kill()
+{
+ <T>SkipBagNode *p = this->header->forward[0];
+
+ while (p != header)
+ {
+ <T>SkipBagNodePtr q = p->forward[0];
+ delete p;
+ p = q;
+ }
+}
+
+void <T>SkipBag::clear()
+{
+ <T>SkipBagNodePtr *buffer_start = header->forward;
+ <T>SkipBagNodePtr *trav = &header->forward[level+1];
+ _kill();
+ count = 0;
+
+ while (trav > buffer_start)
+ *--trav = (<T>SkipBagNodePtr)header;
+}
+
+Pix <T>SkipBag::seek(<T&> key, Pix i)
+{
+ <T>SkipBagNodePtr temp;
+ <T>SkipBagNode *curr = header;
+ int l = level;
+ if (i)
+ curr = (<T>SkipBagNode *)i;
+
+ do
+ {
+ while ((temp = curr->forward[l])!=header &&
+ <T>CMP(temp->item, key) < 0)
+ curr = temp;
+ }
+ while (--l >= 0);
+
+ if (<T>CMP(temp->item, key) != 0)
+ return 0;
+ else
+ {
+ return Pix(temp);
+ }
+}
+
+
+int <T>SkipBag::nof(<T&> item)
+{
+ int n = 0;
+ <T>SkipBagNodePtr t = (<T>SkipBagNodePtr)(seek(item));
+ if (t != 0)
+ {
+ do
+ {
+ ++n;
+ t = succ(t);
+ } while (t != 0 && <T>EQ(item, t->item));
+ }
+ return n;
+}
+
+void <T>SkipBag::remove(<T&> key)
+{
+ Pix t = seek(key);
+ while (t != 0)
+ {
+ del(key);
+ t = seek(key);
+ }
+}
+
+
+/*
+ * random function for probabilistic balancing
+ *
+ * Hardwired for p = .25. Not too flexible,
+ * but fast. Changing this would require a constructor
+ * that would accept a different value for p, etc.
+ * Perhaps someone else would like to implement this?
+ *
+ */
+int <T>SkipBag::random_level (void)
+{
+ int rlevel = 0;
+ int b;
+
+ do
+ {
+ b = random_bits & 3L;
+ if (!b)
+ rlevel++;
+ random_bits >>= 2;
+ if (--randoms_left == 0)
+ {
+ random_bits = gen->asLong();
+ randoms_left = BITS_IN_RANDOM / 2;
+ };
+ }
+ while (!b);
+
+ return rlevel > max_levels ? max_levels : rlevel;
+}
+
+int <T>SkipBag::OK()
+{
+ int v = 1;
+ if (header == 0)
+ v = 0;
+ else
+ {
+ int n = 0;
+ <T>SkipBagNodePtr trail = leftmost();
+ <T>SkipBagNodePtr t = 0;
+ if (trail) t = succ(trail);
+ if (t) n++;
+ while (t != 0)
+ {
+ ++n;
+ v &= <T>CMP(trail->item, t->item) < 0;
+ trail = t;
+ t = succ(t);
+ }
+ v &= n == count;
+ }
+ if (!v) error("invariant failure");
+ return v;
+}
+
+<T>SkipBaginit::<T>SkipBaginit()
+{
+ if (!count)
+ <T>SkipBag::gen = new MLCG(time(0));
+ count++;
+}
+
+<T>SkipBaginit::~<T>SkipBaginit()
+{
+ count--;
+ if (!count)
+ delete <T>SkipBag::gen;
+}
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