Category : OS/2 Files
Archive   : GPPDEV8F.ZIP
Filename : SKIPSET.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.
*/

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

#include
#include

#include ".SkipSet.h"

MLCG* SkipSet::gen = 0;
int SkipSetinit::count = 0;

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

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

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

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

count = 0;

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

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

/* relationals */

int SkipSet::operator == (SkipSet& y)
{
if (count != y.count)
return 0;
else
{
SkipSetNodePtr t = leftmost();
SkipSetNodePtr u = y.leftmost();
for (;;)
{
if (t == 0)
return 1;
else if (!EQ(t->item, u->item))
return 0;
else
{
t = succ(t);
u = y.succ(u);
}
}
}
}

int SkipSet::operator <= (SkipSet& y)
{
if (count > y.count)
return 0;
else
{
SkipSetNodePtr t = leftmost();
SkipSetNodePtr u = y.leftmost();
for (;;)
{
if (t == 0)
return 1;
else if (u == 0)
return 0;
int cmp = CMP(t->item, u->item);
if (cmp == 0)
{
t = succ(t);
u = y.succ(u);
}
else if (cmp < 0)
return 0;
else
u = y.succ(u);
}
}
}


void SkipSet::operator |=(SkipSet& y)
{
if (&y == this) return;
SkipSetNodePtr u = y.leftmost();
while (u != 0)
{
add(u->item);
u = y.succ(u);
}
}

void SkipSet::operator &= (SkipSet& y)
{
if (y.count == 0)
clear();
else if (&y != this && count != 0)
{
SkipSetNodePtr t = leftmost();
while (t != 0)
{
SkipSetNodePtr s = succ(t);
if (y.seek(t->item) == 0) del(t->item);
t = s;
}
}
}


void SkipSet::operator -=(SkipSet& y)
{
if (&y == this)
clear();
else if (y.count != 0)
{
SkipSetNodePtr t = leftmost();
while (t != 0)
{
SkipSetNodePtr s = succ(t);
if (y.seek(t->item) != 0) del(t->item);
t = s;
}
}
}

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

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

if (temp != header && CMP(temp->item, i) == 0)
return Pix(temp);

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

temp = new RealSkipSetNode (i, l);
SkipSetNodePtr *temp_forward = temp->forward;

do
{
SkipSetNodePtr *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 SkipSet::del( key)
{

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

SkipSetNodePtr *forward = header->forward;

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

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

SkipSetNodePtr SkipSet::rightmost()
{
SkipSetNodePtr temp;
SkipSetNode* curr = header;
int l = level;

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

return temp==header ? 0 : temp;
}

SkipSetNodePtr SkipSet::pred(SkipSetNodePtr t)
{
SkipSetNodePtr temp, curr = (SkipSetNodePtr) header;
int l = level;

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

return curr == header ? 0 : curr;
}

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

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

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

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

Pix SkipSet::seek( key)
{
SkipSetNodePtr temp;
SkipSetNode *curr = header;
int l = level;

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);
}
}


/*
* 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 SkipSet::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 SkipSet::OK()
{
int v = 1;
if (header == 0)
v = 0;
else
{
int n = 0;
SkipSetNodePtr trail = leftmost();
SkipSetNodePtr 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;
}

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

SkipSetinit::~SkipSetinit()
{
count--;
if (!count)
delete SkipSet::gen;
}