Botan::Fixed_Window_Exponentiator Class Reference

#include <def_powm.h>

Inheritance diagram for Botan::Fixed_Window_Exponentiator:

Public Member Functions
Modular_Exponentiator *	copy () const override
BigInt	execute () const override
	Fixed_Window_Exponentiator (const BigInt &, Power_Mod::Usage_Hints)
void	set_base (const BigInt &) override
void	set_exponent (const BigInt &) override

Detailed Description

Fixed Window Exponentiator

Definition at line 20 of file def_powm.h.

Constructor & Destructor Documentation

Botan::Fixed_Window_Exponentiator::Fixed_Window_Exponentiator	(	const BigInt &	n,
		Power_Mod::Usage_Hints	hints
	)

Definition at line 61 of file powm_fw.cpp.

Referenced by copy().

      : m_reducer{Modular_Reducer(n)}, m_exp{}, m_window_bits{}, m_g{}, m_hints{hints}
   {}

Member Function Documentation

Modular_Exponentiator* Botan::Fixed_Window_Exponentiator::copy ( ) const

inlineoverridevirtual

Implements Botan::Modular_Exponentiator.

Definition at line 27 of file def_powm.h.

References Fixed_Window_Exponentiator().

         { return new Fixed_Window_Exponentiator(*this); }

BigInt Botan::Fixed_Window_Exponentiator::execute ( ) const

overridevirtual

Implements Botan::Modular_Exponentiator.

Definition at line 40 of file powm_fw.cpp.

References Botan::BigInt::bits(), Botan::BigInt::get_substring(), Botan::Modular_Reducer::multiply(), and Botan::Modular_Reducer::square().

   {
   const size_t exp_nibbles = (m_exp.bits() + m_window_bits - 1) / m_window_bits;

   BigInt x = 1;

   for(size_t i = exp_nibbles; i > 0; --i)
      {
      for(size_t j = 0; j != m_window_bits; ++j)
         x = m_reducer.square(x);

      const uint32_t nibble = m_exp.get_substring(m_window_bits*(i-1), m_window_bits);

      x = m_reducer.multiply(x, m_g[nibble]);
      }
   return x;
   }

void Botan::Fixed_Window_Exponentiator::set_base ( const BigInt &  base )

overridevirtual

Implements Botan::Modular_Exponentiator.

Definition at line 25 of file powm_fw.cpp.

References Botan::BigInt::bits(), Botan::Modular_Reducer::multiply(), and Botan::Power_Mod::window_bits().

   {
   m_window_bits = Power_Mod::window_bits(m_exp.bits(), base.bits(), m_hints);

   m_g.resize((1 << m_window_bits));
   m_g[0] = 1;
   m_g[1] = base;

   for(size_t i = 2; i != m_g.size(); ++i)
      m_g[i] = m_reducer.multiply(m_g[i-1], m_g[1]);
   }

void Botan::Fixed_Window_Exponentiator::set_exponent ( const BigInt &  e )

overridevirtual

Implements Botan::Modular_Exponentiator.

Definition at line 17 of file powm_fw.cpp.

   {
   m_exp = e;
   }

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The documentation for this class was generated from the following files:

• src/lib/math/numbertheory/def_powm.h
• src/lib/math/numbertheory/powm_fw.cpp