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//
// aegis - project change supervisor
// Copyright (C) 2004-2008 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/error.h> // for assert
#include <common/mem.h>
#include <common/symtab.h>
void
symtab_ty::split()
{
//
// 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 symtab. 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 symtab.
//
str_hash_ty new_hash_modulus = hash_modulus * 2;
str_hash_ty new_hash_mask = new_hash_modulus - 1;
row_t **new_hash_table = new row_t * [new_hash_modulus];
//
// now redistribute the list elements
//
for (str_hash_ty idx = 0; idx < hash_modulus; ++idx)
{
new_hash_table[idx] = 0;
new_hash_table[idx + hash_modulus] = 0;
row_t *p = hash_table[idx];
while (p)
{
row_t *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.get_hash() & hash_mask) == idx);
str_hash_ty idx2 = p2->key.get_hash() & new_hash_mask;
row_t **ipp = &new_hash_table[idx2];
for (; *ipp; ipp = &(*ipp)->overflow)
;
*ipp = p2;
}
}
delete [] hash_table;
hash_table = new_hash_table;
hash_modulus = new_hash_modulus;
hash_mask = new_hash_mask;
}
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