count-min-sketch.H

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/*
                          Aleph_w
 
  Data structures & Algorithms
  version 2.0.0b
  https://github.com/lrleon/Aleph-w
 
  This file is part of Aleph-w library
 
  Copyright (c) 2002-2026 Leandro Rabindranath Leon
 
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
 
  The above copyright notice and this permission notice shall be included in all
  copies or substantial portions of the Software.
 
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
*/
 
# ifndef COUNT_MIN_SKETCH_H
# define COUNT_MIN_SKETCH_H
 
# include <cmath>
# include <algorithm>
# include <concepts>
# include <cstdint>
# include <limits>
 
# include <ah-errors.H>
# include <tpl_array.H>
# include <hash-fct.H>
 
namespace Aleph
{
 
  template <typename T, std::unsigned_integral CounterT = size_t>
  class Count_Min_Sketch
  {
    size_t w_;             
    size_t d_;             
    Array<CounterT> table_; 
    Array<uint32_t> seeds_; 
    CounterT total_count_ = 0; 
  public:
    Count_Min_Sketch(const size_t w, const size_t d)
      : w_(w), d_(d)
    {
      ah_domain_error_if(w == 0 or d == 0) 
        << "Count_Min_Sketch: dimensions must be positive";
 
      ah_domain_error_if(w > std::numeric_limits<size_t>::max() / d)
        << "Count_Min_Sketch: product of dimensions w*d overflows size_t (got "
        << w << " * " << d << ")";
      
      table_ = Array<CounterT>(w_ * d_, CounterT(0));
      seeds_.reserve(d_);
      
      for (size_t i = 0; i < d_; ++i)
        seeds_.append(static_cast<uint32_t>(dft_hash_fct(i, 0x9e3779b9)));
    }
 
    static Count_Min_Sketch from_error_bounds(const double epsilon, const double delta)
    {
      ah_domain_error_if(epsilon <= 0.0 or not std::isfinite(epsilon)) 
        << "Count_Min_Sketch::from_error_bounds: epsilon must be positive and finite (got " << epsilon << ")";
      ah_domain_error_if(delta <= 0.0 or delta >= 1.0 or not std::isfinite(delta))
        << "Count_Min_Sketch::from_error_bounds: delta must be in (0, 1) and finite (got " << delta << ")";
 
      const double w_dbl = std::ceil(std::exp(1.0) / epsilon);
      const double d_dbl = std::ceil(std::log(1.0 / delta));
      const double max_sz = static_cast<double>(std::numeric_limits<size_t>::max());
 
      ah_domain_error_if(w_dbl > max_sz or d_dbl > max_sz)
        << "Count_Min_Sketch::from_error_bounds: calculated dimensions exceed size_t limits";
 
      return Count_Min_Sketch(static_cast<size_t>(w_dbl), static_cast<size_t>(d_dbl));
    }
 
    void update(const T & val, CounterT count = 1)
    {
      if (count == 0) return;
 
      constexpr CounterT max_val = std::numeric_limits<CounterT>::max();
 
      for (size_t i = 0; i < d_; ++i)
        {
          const size_t h = murmur3hash(val, seeds_[i]) % w_;
          const size_t idx = i * w_ + h;
          if (max_val - table_[idx] < count)
            table_(idx) = max_val;
          else
            table_(idx) += count;
        }
 
      if (max_val - total_count_ < count)
        total_count_ = max_val;
      else
        total_count_ += count;
    }
 
    [[nodiscard]] CounterT estimate(const T & val) const
    {
      CounterT min_val = std::numeric_limits<CounterT>::max();
      for (size_t i = 0; i < d_; ++i)
        {
          const size_t h = murmur3hash(val, seeds_[i]) % w_;
          min_val = std::min(min_val, table_[i * w_ + h]);
        }
      return min_val;
    }
 
    void merge(const Count_Min_Sketch & other)
    {
      ah_domain_error_if(w_ != other.w_ or d_ != other.d_)
        << "Count_Min_Sketch::merge: dimension mismatch";
      
      for (size_t i = 0; i < d_; ++i)
        ah_domain_error_if(seeds_(i) != other.seeds_[i])
          << "Count_Min_Sketch::merge: hash seed mismatch at index " << i;
      
      constexpr CounterT max_val = std::numeric_limits<CounterT>::max();
 
      for (size_t i = 0; i < table_.size(); ++i)
        {
          if (max_val - table_[i] < other.table_[i])
            table_(i) = max_val;
          else
            table_(i) += other.table_[i];
        }
      
      if (max_val - total_count_ < other.total_count_)
        total_count_ = max_val;
      else
        total_count_ += other.total_count_;
    }
 
    void clear()
    {
      for (size_t i = 0; i < table_.size(); ++i)
        table_(i) = 0;
      total_count_ = 0;
    }
 
    [[nodiscard]] size_t width() const noexcept { return w_; }
 
    [[nodiscard]] size_t depth() const noexcept { return d_; }
 
    [[nodiscard]] CounterT total_count() const noexcept { return total_count_; }
  };
 
} // namespace Aleph
 
# endif // COUNT_MIN_SKETCH_H