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/**
* Entropy Accumulator
* (C) 1999-2009 Jack Lloyd
*/
#include <botan/entropy_src.h>
namespace Botan {
void Entropy_Accumulator::reset_goal(u32bit entropy_goal)
{
goal_bits = entropy_goal;
collected_bits = 0;
/*
* The buffer is large enough to hold 2*goal_bits of entropy,
* or 128 bits, whichever is larger
*/
entropy_buf.create(std::max<u32bit>(goal_bits / 4, 16));
io_buffer.destroy();
}
MemoryRegion<byte>& Entropy_Accumulator::get_io_buffer(u32bit size)
{
io_buffer.create(size);
return io_buffer;
}
u32bit Entropy_Accumulator::desired_remaining_bits() const
{
if(collected_bits >= goal_bits)
return 0;
return (goal_bits - collected_bits);
}
bool Entropy_Accumulator::polling_goal_achieved() const
{
return (collected_bits >= goal_bits);
}
void Entropy_Accumulator::add(const void* in_void,
u32bit length,
double entropy_bits_per_byte)
{
if(length == 0)
return;
entropy_bits_per_byte = std::max(0.0, std::min(entropy_bits_per_byte, 8.0));
const byte* in = static_cast<const byte*>(in_void);
u32bit buf_i = 0; // write index into entropy_buf
u32bit bytes_collected = 0;
byte last = 0;
byte count = 0;
for(u32bit i = 0; i != length; ++i)
{
if(in[i] != last) // run length encode the input
{
entropy_buf[buf_i] ^= last;
buf_i = (buf_i + 1) % entropy_buf.size();
if(count > 1)
{
entropy_buf[buf_i] ^= count;
buf_i = (buf_i + 1) % entropy_buf.size();
}
++bytes_collected;
last = in[i];
count = 1;
}
else
++count;
}
entropy_buf[0] ^= last;
entropy_buf[1] ^= count;
collected_bits += static_cast<u32bit>(entropy_bits_per_byte * bytes_collected);
collected_bits = std::min(collected_bits, 8 * entropy_buf.size());
}
}
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