BitMagic-C++
sample11.cpp

Example of how to use various bit counting techniques

See also
bm::bvector<>::count()
bm::bvector<>::count_range()
bm::bvector<>::count_to()
bm::count_and()
bm::bvector<>::counted_enumerator
/*
Copyright(c) 2002-2017 Anatoliy Kuznetsov(anatoliy_kuznetsov at yahoo.com)
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
For more information please visit: http://bitmagic.io
*/
/** \example sample11.cpp
Example of how to use various bit counting techniques
\sa bm::bvector<>::count()
\sa bm::bvector<>::count_range()
\sa bm::bvector<>::count_to()
\sa bm::count_and()
\sa bm::bvector<>::counted_enumerator
*/
/*! \file sample11.cpp
\brief Example: bvector<> bit-counting techniques analysis
*/
#include <iostream>
#include <random>
#include <memory>
#include "bm.h"
#include "bmalgo.h"
#include "bmtimer.h"
#include "bmundef.h" /* clear the pre-proc defines from BM */
using namespace std;
// timing storage for benchmarking
const unsigned benchmark_count = 10000;
unsigned vector_max = 400000000;
std::random_device rand_dev;
std::mt19937 gen(rand_dev()); // mersenne_twister_engine
std::uniform_int_distribution<> rand_dis(1, int(vector_max)); // generate uniform numebrs for [1, vector_max]
/// generate pseudo-random bit-vector, mix of blocks
///
static
{
for (i = 0; i < vector_max;)
{
// generate bit-blocks
for (j = 0; j < 65535*8; i += 10, j++)
{
bv.set(i);
}
if (i > vector_max)
break;
// generate GAP (compressed) blocks
for (j = 0; j < 65535; i += 120, j++)
{
unsigned len = rand() % 64;
bv.set_range(i, i + len);
i += len;
if (i > vector_max)
break;
}
}
// compress vector
bv.optimize(tb);
// compute bit-vector statistics
bv.calc_stat(&st);
std::cout << "Bit-vector statistics: GAP (compressed blocks)=" << st.gap_blocks
<< ", BIT (uncompressed blocks)=" << st.bit_blocks
<< std::endl << std::endl;
}
/// "pre-heat" CPU to minimize dynamic overclocking effects
///
static
{
for (unsigned i = 0; i < benchmark_count; ++i)
{
cnt += bv.count();
m+=cnt*cnt;
}
return m;
}
/// simple population count for the whole vector
///
static
{
{
bm::chrono_taker tt1("1. bvector<>::count()", benchmark_count / 2, &timing_map);
for (unsigned i = 0; i < benchmark_count / 2; ++i)
{
cnt += bv.count();
}
}
// this is mostly to prevent compiler to optimize loop away
std::cout << "Count test finished." << cnt << "\r";
}
/// count_range() test
///
static
{
{
bm::chrono_taker tt1("2. bvector<>::count_range()", benchmark_count, &timing_map);
for (unsigned i = 0; i < benchmark_count; ++i)
{
unsigned from = unsigned(rand_dis(gen));
unsigned to = unsigned(rand_dis(gen));
if (from > to)
swap(from, to);
cnt += bv.count_range(from, to);
}
}
// this is mostly to prevent compiler to optimize loop away
std::cout << "Count range test finished." << cnt << "\r";
}
/// count_range() test using pre-calculated blocks bit count
///
static
{
std::unique_ptr<bm::bvector<>::rs_index_type> rs(new bm::bvector<>::rs_index_type());
bv.build_rs_index(rs.get());
{
bm::chrono_taker tt1("3. bvector<>::count_range() with rs_index", benchmark_count, &timing_map);
cnt = 0;
for (unsigned i = 0; i < benchmark_count; ++i)
{
unsigned from = unsigned(rand_dis(gen));
unsigned to = unsigned(rand_dis(gen));
if (from > to)
swap(from, to);
cnt += bv.count_range(from, to, *rs); // use rs index for acceleration
} // for i
}
// this is mostly to prevent compiler to optimize loop away
std::cout << "Count range with blocks test finished." << cnt << "\r";
}
/// count_to() test using pre-calculated rank-select index
///
static
{
// build a block population count list, used for count_to() acceleration
std::unique_ptr<bm::bvector<>::rs_index_type> rs(new bm::bvector<>::rs_index_type());
bv.build_rs_index(rs.get());
{
bm::chrono_taker tt1("4. bvector<>::count_to() with rs_index", benchmark_count, &timing_map);
for (unsigned i = 0; i < benchmark_count; ++i)
{
unsigned to = unsigned(rand_dis(gen));
cnt += bv.count_to(to, *rs); // use rank-select index for acceleration
}
}
// this is mostly to prevent compiler to optimize loop away
std::cout << "Count to with blocks test finished." << cnt << "\r";
}
/// count_range implemented via two count_to() calls using pre-calculated
/// rank-select index
///
static
{
// build a block population count list, used for count_to() acceleration
std::unique_ptr<bm::bvector<>::rs_index_type> rs(new bm::bvector<>::rs_index_type());
bv.build_rs_index(rs.get());
{
bm::chrono_taker tt1("5. bvector<>::count_to to simulate count_range()", benchmark_count, &timing_map);
for (unsigned i = 0; i < benchmark_count; ++i)
{
unsigned from = unsigned(rand_dis(gen));
unsigned to = unsigned(rand_dis(gen));
if (from > to)
swap(from, to);
bm::bvector<>::size_type cnt_to = bv.count_to(to, *rs);
bm::bvector<>::size_type cnt_from = bv.count_to(from - 1, *rs);
bm::bvector<>::size_type cnt_r = cnt_to - cnt_from;
cnt += cnt_r;
}
}
// this is mostly to prevent compiler to optimize loop away
std::cout << "Count range via count_to test finished." << cnt << "\r";
}
/// count_range implemented via bm::count_and
///
/// this method can be used, when we need co compute multiple ranges in one call
///
static
void bv_count_and(const bm::bvector<>& bv)
{
{
bm::chrono_taker tt1("6. bm::count_and with mask vector", benchmark_count, &timing_map);
bm::bvector<> mask_bv(bm::BM_GAP); // use compressed mask, better seluts on long ranges
for (unsigned i = 0; i < benchmark_count; ++i)
{
unsigned from = unsigned(rand_dis(gen));
unsigned to = unsigned(rand_dis(gen));
if (from > to)
swap(from, to);
mask_bv.set_range(from, to, true); // set mask vector
cnt += bm::count_and(bv, mask_bv);
mask_bv.clear(true); // clear and free memory (faster)
}
}
// this is mostly to prevent compiler to optimize loop away
std::cout << "count AND finished." << cnt << "\r";
}
/// count_to implemented via bm::bvector<>::counted_enumerator
///
/// Counted enumerator is an iterator automata, which counts the running population count
/// along the iteration sequence
///
static
{
{
// This is a slow method so we use less iterators
bm::chrono_taker tt1("7. bm::bvector<>::counted_enumerator", benchmark_count/20, &timing_map);
for (unsigned i = 0; i < benchmark_count/20; ++i)
{
unsigned to = unsigned(rand_dis(gen));
for (; en.valid(); ++en)
{
if (*en > to)
break;
}
cnt += en.count();
}
}
std::cout << "counted_enumerator finished." << cnt << "\r";
}
int main(void)
{
try
{
/// pre-heat CPU to minimize dynamic overclocking
unsigned s = pre_heat(bv);
std::cout << s << "\r";
// Test 1.
// Uses plain bvector<>::count() to compute global population count
// This function would benefit from SIMD (SSE42 / AVX2) acceleration
//
// Test 2.
// Uses bvector<>::count_range() to compute population count in a randomly generated
// region of a bit-vector.
// This is should be naturally faster than Test 1, because it range is less than the whole
//
// Test 3.
// Uses bvector<>::count_range() together with bvector<>::count_blocks()
// (pre-calculated bit-count for each block).
// It make sense to use this method if bit-vector is constant (or chnages infrequently)
// and we need to do many range counting calculations
//
// Test 4.
// Uses bvector<>::count_to() to compute population count to a specified element.
// Equivalent of count_range(0, to);
// This method uses acceleration structure using bvector<>::running_count_blocks()
// It is similar to count_range acceleration, but uses a different (faster) algorithm
//
// Test 5.
// Uses bvector<>::count_to() twice to simulate count_range()
// using counting difference:
// count_r = count_to(0, from) - count_to(0, to-1)
// This method can actually be faster than count_range()
//
// Test 6.
// Compute range population count via a mask vector and logical AND operation.
// Not the fastest method, but can be useful, when multiple ranges needs to be computed
//
// Test 7.
// Compute cout using counted_enumerator iterator
// method combines iteratrion over bit vector and sliding population count
// print all test timing results
//
std::cout << " "
<< std::endl;
}
catch(std::exception& ex)
{
std::cerr << ex.what() << std::endl;
return 1;
}
return 0;
}