/* Copyright 2013 IST Austria
Contributed by: Hubert Wagner
This file is part of PHAT.
PHAT is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
PHAT 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 Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with PHAT. If not, see . */
#pragma once
#include
#include
namespace phat {
// This is a bitset indexed with a 64-ary tree. Each node in the index
// has 64 bits; i-th bit says that the i-th subtree is non-empty.
// Supports practically O(1), inplace, zero-allocation: insert, remove, max_element
// and clear in O(number of ones in the bitset).
// 'add_index' is still the real bottleneck in practice.
class bit_tree_column
{
protected:
size_t offset; // data[i + offset] = ith block of the data-bitset
typedef uint64_t block_type;
std::vector< block_type > data;
size_t debrujin_magic_table[ 64 ];
enum { block_size_in_bits = 64 };
enum { block_shift = 6 };
// Some magic: http://graphics.stanford.edu/~seander/bithacks.html
// Gets the position of the rightmost bit of 'x'. 0 means the most significant bit.
// (-x)&x isolates the rightmost bit.
// The whole method is much faster than calling log2i, and very comparable to using ScanBitForward/Reverse intrinsic,
// which should be one CPU instruction, but is not portable.
size_t rightmost_pos( const block_type value ) const {
return 64 - 1 - debrujin_magic_table[ ( (value & (-(int64_t)value) ) * 0x07EDD5E59A4E28C2 ) >> 58 ];
}
public:
void init( index num_cols ) {
int64_t n = 1; // in case of overflow
int64_t bottom_blocks_needed = ( num_cols + block_size_in_bits - 1 ) / block_size_in_bits;
int64_t upper_blocks = 1;
// How many blocks/nodes of index needed to index the whole bitset?
while( n * block_size_in_bits < bottom_blocks_needed ) {
n *= block_size_in_bits;
upper_blocks += n;
}
offset = upper_blocks;
data.resize( upper_blocks + bottom_blocks_needed, 0 );
std::size_t temp_array[ 64 ] = {
63, 0, 58, 1, 59, 47, 53, 2,
60, 39, 48, 27, 54, 33, 42, 3,
61, 51, 37, 40, 49, 18, 28, 20,
55, 30, 34, 11, 43, 14, 22, 4,
62, 57, 46, 52, 38, 26, 32, 41,
50, 36, 17, 19, 29, 10, 13, 21,
56, 45, 25, 31, 35, 16, 9, 12,
44, 24, 15, 8, 23, 7, 6, 5 };
std::copy( &temp_array[ 0 ], &temp_array[ 64 ], &debrujin_magic_table[ 0 ] );
}
index get_max_index() const {
if( !data[ 0 ] )
return -1;
size_t n = 0;
size_t newn = 0;
size_t index = 0;
while( newn < data.size() ) {
n = newn;
index = rightmost_pos( data[ n ] );
newn = ( n << block_shift ) + index + 1;
}
return ( ( n - offset ) << block_shift ) + index;
}
bool is_empty() const {
return data[ 0 ] == 0;
}
void add_index( const size_t entry ) {
const block_type ONE = 1;
const block_type block_modulo_mask = ( ONE << block_shift ) - 1;
size_t index_in_level = entry >> block_shift;
size_t address = index_in_level + offset;
size_t index_in_block = entry & block_modulo_mask;
block_type mask = ( ONE << ( block_size_in_bits - index_in_block - 1 ) );
data[ address ] ^= mask;
// Check if we reached the root. Also, if anyone else was in this block, we don't need to update the path up.
while( address && !( data[ address ] & ~mask ) ) {
index_in_block = index_in_level & block_modulo_mask;
index_in_level >>= block_shift;
--address;
address >>= block_shift;
mask = ( ONE << ( block_size_in_bits - index_in_block - 1 ) );
data[ address ] ^= mask;
}
}
void get_col_and_clear( column &out ) {
index mx = this->get_max_index();
while( mx != -1 ) {
out.push_back( mx );
add_index( mx );
mx = this->get_max_index();
}
std::reverse( out.begin(), out.end() );
}
void add_col(const column &col) {
for( size_t i = 0; i < col.size(); ++i )
add_index(col[i]);
}
void clear() {
index mx = this->get_max_index();
while( mx != -1 ) {
add_index( mx );
mx = this->get_max_index();
}
}
void remove_max() {
add_index( get_max_index() );
}
void set_col( const column& col ) {
clear();
add_col( col );
}
void get_col( column& col ) {
get_col_and_clear( col );
add_col( col );
}
};
typedef abstract_pivot_column bit_tree_pivot_column;
}