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## Class template subtract_with_carry_engine

boost::random::subtract_with_carry_engine

## Synopsis

    // In header: <boost/random/subtract_with_carry.hpp>

    template<typename IntType, std::size_t w, std::size_t s, std::size_t r>
    class subtract_with_carry_engine {
    public:
      // types
      typedef IntType result_type;

      // construct/copy/destruct
      subtract_with_carry_engine();
      explicit subtract_with_carry_engine(IntType);
      template<typename SeedSeq> explicit subtract_with_carry_engine(SeedSeq &);
      template<typename It> subtract_with_carry_engine(It &, It);

      // public member functions
      void seed();
      void seed(IntType);
      template<typename SeedSeq> void seed(SeedSeq &);
      template<typename It> void seed(It &, It);
      result_type operator()();
      void discard(boost::uintmax_t);
      template<typename It> void generate(It, It);

      // public static functions
      static result_type min();
      static result_type max();

      // friend functions
      template<typename CharT, typename Traits>
        friend std::basic_ostream< CharT, Traits > &
        operator<<(std::basic_ostream< CharT, Traits > &,
                   const subtract_with_carry_engine &);
      template<typename CharT, typename Traits>
        friend std::basic_istream< CharT, Traits > &
        operator>>(std::basic_istream< CharT, Traits > &,
                   const subtract_with_carry_engine &);
      friend bool operator==(const subtract_with_carry_engine &,
                             const subtract_with_carry_engine &);
      friend bool operator!=(const subtract_with_carry_engine &,
                             const subtract_with_carry_engine &);

      // public data members
      static const std::size_t word_size;
      static const std::size_t long_lag;
      static const std::size_t short_lag;
      static const uint32_t default_seed;
      static const bool has_fixed_range;
      static const result_type modulus;
    };

## Description

Instantiations of `subtract_with_carry_engine` model a pseudo-random number generator . The algorithm is described in

> "A New Class of Random Number Generators", George Marsaglia and Arif Zaman, Annals of Applied Probability, Volume 1, Number 3 (1991), 462-480.

### `subtract_with_carry_engine` public construct/copy/destruct

1.     subtract_with_carry_engine();

   Constructs a new ``subtract_with_carry_engine`` and seeds it with the default seed.

2.     explicit subtract_with_carry_engine(IntType value);

   Constructs a new ``subtract_with_carry_engine`` and seeds it with `value`.

3.     template<typename SeedSeq> explicit subtract_with_carry_engine(SeedSeq & seq);

   Constructs a new ``subtract_with_carry_engine`` and seeds it with values produced by `seq.generate()`.

4.     template<typename It> subtract_with_carry_engine(It & first, It last);

   Constructs a new ``subtract_with_carry_engine`` and seeds it with values from a range. first is updated to point one past the last value consumed. If there are not enough elements in the range to fill the entire state of the generator, throws `std::invalid_argument`.

### `subtract_with_carry_engine` public member functions

1.     void seed();

   Seeds the generator with the default seed.

2.     void seed(IntType value);

3.     template<typename SeedSeq> void seed(SeedSeq & seq);

   Seeds the generator with values produced by `seq.generate()`.

4.     template<typename It> void seed(It & first, It last);

   Seeds the generator with values from a range. Updates `first` to point one past the last consumed value. If the range does not contain enough elements to fill the entire state of the generator, throws `std::invalid_argument`.

5.     result_type operator()();

   Returns the next value of the generator.

6.     void discard(boost::uintmax_t z);

   Advances the state of the generator by `z`.

7.     template<typename It> void generate(It first, It last);

   Fills a range with random values.

### `subtract_with_carry_engine` public static functions

1.     static result_type min();

   Returns the smallest value that the generator can produce.

2.     static result_type max();

   Returns the largest value that the generator can produce.

### `subtract_with_carry_engine` friend functions

1.     template<typename CharT, typename Traits>
         friend std::basic_ostream< CharT, Traits > &
         operator<<(std::basic_ostream< CharT, Traits > & os,
                    const subtract_with_carry_engine & f);

   Writes a ``subtract_with_carry_engine`` to a `std::ostream`.

2.     template<typename CharT, typename Traits>
         friend std::basic_istream< CharT, Traits > &
         operator>>(std::basic_istream< CharT, Traits > & is,
                    const subtract_with_carry_engine & f);

   Reads a ``subtract_with_carry_engine`` from a `std::istream`.

3.     friend bool operator==(const subtract_with_carry_engine & x,
                              const subtract_with_carry_engine & y);

   Returns true if the two generators will produce identical sequences of values.

4.     friend bool operator!=(const subtract_with_carry_engine & lhs,
                              const subtract_with_carry_engine & rhs);

   Returns true if the two generators will produce different sequences of values.