//
//      aegis - project change supervisor
//      Copyright (C) 1998, 2002-2008, 2012 Peter Miller
//
//      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 3 of the License, 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, see
//      <http://www.gnu.org/licenses/>.
//

#include <common/ac/assert.h>

#include <common/itab.h>
#include <common/mem.h>
#include <common/trace.h>


//
// NAME
//      itab_alloc
//
// SYNOPSIS
//      itab_ty *itabLalloc(int);
//
// DESCRIPTION
//      The itab_alloc function is used to allocate a new integer table
//      instance in dynamic memory.
//
// RETURNS
//      itab_ty *; pointer to table
//
// CAVEAT
//      Use itab_free when you are done with it.
//

itab_ty *
itab_alloc()
{
    itab_ty         *itp;
    itab_key_ty     j;

    trace(("itab_alloc()\n{\n"));
    itp = (itab_ty *)mem_alloc(sizeof(itab_ty));
    itp->reap = 0;
    itp->hash_modulus = 1 << 5; // MUST be a power of 2
    itp->hash_mask = itp->hash_modulus - 1;
    itp->load = 0;
    itp->hash_table =
        (itab_row_ty **)mem_alloc(itp->hash_modulus * sizeof(itab_row_ty *));
    for (j = 0; j < itp->hash_modulus; ++j)
        itp->hash_table[j] = 0;
    trace(("return %p;\n", itp));
    trace(("}\n"));
    return itp;
}


//
// NAME
//      itab_free
//
// SYNOPSIS
//      void itab_free(itab_ty *);
//
// DESCRIPTION
//      The itab_free function is used to release the resources held by
//      an integer table.
//

void
itab_free(itab_ty *itp)
{
    itab_key_ty j;

    trace(("itab_free(itp = %p)\n{\n", itp));
    for (j = 0; j < itp->hash_modulus; ++j)
    {
        itab_row_ty     **rpp;

        rpp = &itp->hash_table[j];
        while (*rpp)
        {
            itab_row_ty     *rp;

            rp = *rpp;
            *rpp = rp->overflow;
            if (itp->reap)
                itp->reap(rp->data);
            mem_free(rp);
        }
    }
    mem_free(itp->hash_table);
    mem_free(itp);
    trace(("}\n"));
}


//
// NAME
//      split - reduce symbol table load
//
// SYNOPSIS
//      void split(itab_ty);
//
// DESCRIPTION
//      The split function is used to split symbols in the bucket indicated by
//      the split point.  The symbols are split between that bucket and the one
//      after the current end of the table.
//
// CAVEAT
//      It is only sensable to do this when the symbol table load exceeds some
//      reasonable threshold.  A threshold of 80% is suggested.
//

static void
split(itab_ty *itp)
{
    itab_row_ty     **new_hash_table;
    itab_key_ty     new_hash_modulus;
    itab_key_ty     new_hash_mask;
    itab_key_ty     idx;

    trace(("split(itp = %p)\n{\n", itp));

    //
    // double the modulus
    //
    // This is subtle.  If we only increase the modulus by one, the
    // load always hovers around 80%, so we have to do a split for
    // every insert.  I.e. the malloc burden os O(n) for the lifetime of
    // the itab.  BUT if we double the modulus, the length of time
    // until the next split also doubles, making the probablity of a
    // split halve, and sigma(2**-n)=1, so the malloc burden becomes O(1)
    // for the lifetime of the itab.
    //
    new_hash_modulus = itp->hash_modulus * 2;
    new_hash_mask = new_hash_modulus - 1;
    new_hash_table =
        (itab_row_ty **)mem_alloc(new_hash_modulus * sizeof(itab_row_ty *));

    //
    // now redistribute the list elements
    //
    for (idx = 0; idx < itp->hash_modulus; ++idx)
    {
        itab_row_ty     *p;

        new_hash_table[idx] = 0;
        new_hash_table[idx + itp->hash_modulus] = 0;

        p = itp->hash_table[idx];
        while (p)
        {
            itab_row_ty     *p2;
            itab_row_ty     **ipp;

            p2 = p;
            p = p2->overflow;
            p2->overflow = 0;

            //
            // It is important to preserve the order of the links because
            // they can be push-down stacks, and to simply add them to the
            // head of the list will reverse the order of the stack!
            //
            assert((p2->key & itp->hash_mask) == idx);
            itab_key_ty idx2 = p2->key & new_hash_mask;
            for (ipp = &new_hash_table[idx2]; *ipp; ipp = &(*ipp)->overflow)
                ;
            *ipp = p2;
        }
    }
    mem_free(itp->hash_table);
    itp->hash_table = new_hash_table;
    itp->hash_modulus = new_hash_modulus;
    itp->hash_mask = new_hash_mask;
    trace(("}\n"));
}


//
// NAME
//      itab_query - search for a variable
//
// SYNOPSIS
//      int itab_query(itab_ty *, string_ty *key);
//
// DESCRIPTION
//      The itab_query function is used to reference a variable.
//
// RETURNS
//      If the variable has been defined, the function returns a non-zero value
//      and the value is returned through the 'value' pointer.
//      If the variable has not been defined, it returns zero,
//      and 'value' is unaltered.
//

void *
itab_query(itab_ty *itp, itab_key_ty key)
{
    itab_key_ty     idx;
    itab_row_ty     *p;
    void            *result;

    trace(("itab_query(itp = %p, key = %ld)\n{\n", itp, (long)key));
    result = 0;
    idx = key & itp->hash_mask;
    for (p = itp->hash_table[idx]; p; p = p->overflow)
    {
        if (key == p->key)
        {
            result = p->data;
            break;
        }
    }
    trace(("return %p;\n", result));
    trace(("}\n"));
    return result;
}


//
// NAME
//      itab_assign - assign a variable
//
// SYNOPSIS
//      void itab_assign(itab_ty *, string_ty *key, void *data);
//
// DESCRIPTION
//      The itab_assign function is used to assign
//      a value to a given variable.
//
// CAVEAT
//      The name is copied, the data is not.
//

void
itab_assign(itab_ty *itp, itab_key_ty key, void *data)
{
    itab_key_ty     idx;
    itab_row_ty     *p;

    trace(("itab_assign(itp = %p, key = %ld, data = %p)\n{\n",
        itp, (long)key, data));
    idx = key & itp->hash_mask;

    for (p = itp->hash_table[idx]; p; p = p->overflow)
    {
        if (key == p->key)
        {
            trace(("modify existing entry\n"));
            if (itp->reap)
                itp->reap(p->data);
            p->data = data;
            goto done;
        }
    }

    trace(("new entry\n"));
    p = (itab_row_ty *)mem_alloc(sizeof(itab_row_ty));
    p->key = key;
    p->overflow = itp->hash_table[idx];
    p->data = data;
    itp->hash_table[idx] = p;

    itp->load++;
    if (itp->load * 10 >= itp->hash_modulus * 8)
        split(itp);
    done:
    trace(("}\n"));
}


//
// NAME
//      itab_delete - delete a variable
//
// SYNOPSIS
//      void itab_delete(string_ty *name, itab_class_ty class);
//
// DESCRIPTION
//      The itab_delete function is used to delete variables.
//
// CAVEAT
//      The name is freed, the data is reaped.
//      (By default, reap does nothing.)
//

void
itab_delete(itab_ty *itp, itab_key_ty key)
{
    itab_key_ty idx;
    itab_row_ty **pp;

    trace(("itab_delete(itp = %p, key = %ld)\n{\n",
        itp, (long)key));
    idx = key & itp->hash_mask;

    pp = &itp->hash_table[idx];
    for (;;)
    {
        itab_row_ty     *p;

        p = *pp;
        if (!p)
            break;
        if (key == p->key)
        {
            if (itp->reap)
                itp->reap(p->data);
            *pp = p->overflow;
            mem_free(p);
            itp->load--;
            break;
        }
        pp = &p->overflow;
    }
    trace(("}\n"));
}


//
// NAME
//      itab_walk
//
// SYNOPSIS
//      void itab_walk(itab_ty *, void (*)(itab_ty *, itab_key_ty, void *,
//              void *), void *);
//
// DESCRIPTION
//      The itab_walk function is used to visit each element of an
//      integer table, in no particular order.
//

void
itab_walk(itab_ty *itp, void (*func)(itab_ty *, itab_key_ty, void *, void *),
    void *arg)
{
    long            j;
    itab_row_ty     *rp;

    trace(("itab_walk(itp = %p)\n{\n", itp));
    for (j = 0; j < itp->hash_modulus; ++j)
        for (rp = itp->hash_table[j]; rp; rp = rp->overflow)
            func(itp, rp->key, rp->data, arg);
    trace(("}\n"));
}


// vim: set ts=8 sw=4 et :