Category : OS/2 Files
Archive   : GPPDEV8F.ZIP
Filename : SKIPBAG.CCP

// 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, 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/*
* Bags implemented via William Pugh SkipList algorithms.
* CACM, June 1990, p 668-676.
*
*/

#include
#include
#include ".SkipBag.h"

MLCG* SkipBag::gen = 0;
int SkipBaginit::count = 0;

static int countbits(long bits)
{
int n = 0;
while(bits>>=1L) n++;
return n;
}

SkipBag::SkipBag(long size)
: level(0),
header(new SkipBagNode (countbits(size)+1)),
max_levels (countbits(size)+1),
random_bits(gen->asLong()),
randoms_left(BITS_IN_RANDOM / 2)
{
SkipBagNodePtr *buffer_start = header->forward;
SkipBagNodePtr *trav = &header->forward[max_levels];

count = 0;
while (trav > buffer_start)
*--trav = (SkipBagNodePtr) header;
}

SkipBag::SkipBag(SkipBag& b)
: level (0),
header (new SkipBagNode (b.max_levels)),
max_levels (b.max_levels),
random_bits (gen->asLong()),
randoms_left (BITS_IN_RANDOM / 2)
{
SkipBagNodePtr *buffer_start = header->forward;
SkipBagNodePtr *trav = &header->forward[max_levels];

count = 0;

while (trav > buffer_start)
*--trav = (SkipBagNodePtr)header;

for (SkipBagNodePtr t = b.leftmost(); t; t = b.succ(t))
add(t->item);
}

Pix SkipBag::add ( item)
{
SkipBagNodePtr *update = new SkipBagNodePtr[max_levels+1];
SkipBagNodePtr curr = (SkipBagNodePtr) this->header;
int l = level;
SkipBagNodePtr temp;

do
{
while ((temp = curr->forward[l])!=header &&
CMP(temp->item, item) < 0)
curr = temp;
update[l] = curr;
}
while (--l >= 0);

if ((l = random_level ()) > level)
{
l = ++level;
update[l] = (SkipBagNodePtr)header;
};

temp = new RealSkipBagNode (item, l);
SkipBagNodePtr *temp_forward = temp->forward;

do
{
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 SkipBag::del( key)
{

int l = level;
int curr_level = level;
SkipBagNodePtr *update = new SkipBagNodePtr[max_levels+1];
SkipBagNodePtr curr = (SkipBagNodePtr)header;
SkipBagNodePtr temp;

do
{
while ((temp = curr->forward[l])!=header
&& CMP(temp->item,key) < 0)
curr = temp;
update[l] = curr;
}
while (--l >= 0);

if (CMP(temp->item,key)==0)
{
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;

SkipBagNodePtr *forward = header->forward;

while (forward[curr_level]==header && curr_level > 0)
curr_level--;

level = curr_level;
count--;
delete update;
return;
}
}

SkipBagNodePtr SkipBag::rightmost()
{
SkipBagNodePtr temp;
SkipBagNode* curr = header;
int l = level;

do
while ((temp = curr->forward[l])!=header)
curr = temp;
while (--l >= 0);

return temp==header ? 0 : temp;
}

SkipBagNodePtr SkipBag::pred(SkipBagNodePtr t)

{
SkipBagNodePtr temp, curr = (SkipBagNodePtr) header;
int l = level;

do
while ((temp = curr->forward[l])!=t)
curr = temp;
while (--l >= 0);

return curr == header ? 0 : curr;
}

void SkipBag::_kill()
{
SkipBagNode *p = this->header->forward[0];

while (p != header)
{
SkipBagNodePtr q = p->forward[0];
delete p;
p = q;
}
}

void SkipBag::clear()
{
SkipBagNodePtr *buffer_start = header->forward;
SkipBagNodePtr *trav = &header->forward[level+1];
_kill();
count = 0;

while (trav > buffer_start)
*--trav = (SkipBagNodePtr)header;
}

Pix SkipBag::seek( key, Pix i)
{
SkipBagNodePtr temp;
SkipBagNode *curr = header;
int l = level;
if (i)
curr = (SkipBagNode *)i;

do
{
while ((temp = curr->forward[l])!=header &&
CMP(temp->item, key) < 0)
curr = temp;
}
while (--l >= 0);

if (CMP(temp->item, key) != 0)
return 0;
else
{
return Pix(temp);
}
}


int SkipBag::nof( item)
{
int n = 0;
SkipBagNodePtr t = (SkipBagNodePtr)(seek(item));
if (t != 0)
{
do
{
++n;
t = succ(t);
} while (t != 0 && EQ(item, t->item));
}
return n;
}

void SkipBag::remove( 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 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 SkipBag::OK()
{
int v = 1;
if (header == 0)
v = 0;
else
{
int n = 0;
SkipBagNodePtr trail = leftmost();
SkipBagNodePtr t = 0;
if (trail) t = succ(trail);
if (t) n++;
while (t != 0)
{
++n;
v &= CMP(trail->item, t->item) < 0;
trail = t;
t = succ(t);
}
v &= n == count;
}
if (!v) error("invariant failure");
return v;
}

SkipBaginit::SkipBaginit()
{
if (!count)
SkipBag::gen = new MLCG(time(0));
count++;
}

SkipBaginit::~SkipBaginit()
{
count--;
if (!count)
delete SkipBag::gen;
}