buf_filt.cpp

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/*
* Buffered Filter
* (C) 1999-2007 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#include <botan/filters.h>
#include <botan/mem_ops.h>
#include <botan/internal/rounding.h>
#include <botan/exceptn.h>

namespace Botan {

/*
* Buffered_Filter Constructor
*/
Buffered_Filter::Buffered_Filter(size_t b, size_t f) :
   m_main_block_mod(b), m_final_minimum(f)
   {
   if(m_main_block_mod == 0)
      throw Invalid_Argument("m_main_block_mod == 0");

   if(m_final_minimum > m_main_block_mod)
      throw Invalid_Argument("m_final_minimum > m_main_block_mod");

   m_buffer.resize(2 * m_main_block_mod);
   m_buffer_pos = 0;
   }

/*
* Buffer input into blocks, trying to minimize copying
*/
void Buffered_Filter::write(const uint8_t input[], size_t input_size)
   {
   if(!input_size)
      return;

   if(m_buffer_pos + input_size >= m_main_block_mod + m_final_minimum)
      {
      size_t to_copy = std::min<size_t>(m_buffer.size() - m_buffer_pos, input_size);

      copy_mem(&m_buffer[m_buffer_pos], input, to_copy);
      m_buffer_pos += to_copy;

      input += to_copy;
      input_size -= to_copy;

      size_t total_to_consume =
         round_down(std::min(m_buffer_pos,
                             m_buffer_pos + input_size - m_final_minimum),
                    m_main_block_mod);

      buffered_block(m_buffer.data(), total_to_consume);

      m_buffer_pos -= total_to_consume;

      copy_mem(m_buffer.data(), m_buffer.data() + total_to_consume, m_buffer_pos);
      }

   if(input_size >= m_final_minimum)
      {
      size_t full_blocks = (input_size - m_final_minimum) / m_main_block_mod;
      size_t to_copy = full_blocks * m_main_block_mod;

      if(to_copy)
         {
         buffered_block(input, to_copy);

         input += to_copy;
         input_size -= to_copy;
         }
      }

   copy_mem(&m_buffer[m_buffer_pos], input, input_size);
   m_buffer_pos += input_size;
   }

/*
* Finish/flush operation
*/
void Buffered_Filter::end_msg()
   {
   if(m_buffer_pos < m_final_minimum)
      throw Invalid_State("Buffered filter end_msg without enough input");

   size_t spare_blocks = (m_buffer_pos - m_final_minimum) / m_main_block_mod;

   if(spare_blocks)
      {
      size_t spare_bytes = m_main_block_mod * spare_blocks;
      buffered_block(m_buffer.data(), spare_bytes);
      buffered_final(&m_buffer[spare_bytes], m_buffer_pos - spare_bytes);
      }
   else
      {
      buffered_final(m_buffer.data(), m_buffer_pos);
      }

   m_buffer_pos = 0;
   }

}