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/* Copyright (C) Teemu Suutari */
#ifndef FREQUENCYTREE_HPP
#define FREQUENCYTREE_HPP
#include <cstddef>
#include <cstdint>
#include <type_traits>
#include <array>
// For exception
#include "Decompressor.hpp"
namespace ancient::internal
{
template<typename T,typename U,size_t V>
class FrequencyTree
{
public:
FrequencyTree() noexcept
{
for (uint32_t i=0;i<_size;i++)
_tree[i]=0;
}
~FrequencyTree() noexcept=default;
U decode(T value,T &low,T &freq) const
{
if (value>=_tree[_size-1])
throw Decompressor::DecompressionError();
U symbol{0};
low=0;
for (uint32_t i=_levels-2;;i--)
{
T tmp{_tree[_levelOffsets[i]+symbol]};
if (uint32_t(symbol+1)<_levelSizes[i] && value>=tmp)
{
symbol++;
low+=tmp;
value-=tmp;
}
if (!i) break;
symbol<<=1;
}
freq=_tree[symbol];
return symbol;
}
template <typename F>
void onNotZero(F func)
{
uint32_t step{1U<<(_levels-1)};
uint32_t level{_levels-1};
for (uint32_t symbol=0;symbol<V;)
{
while (_tree[_levelOffsets[level]+(symbol>>level)])
{
if (level)
{
level--;
step>>=1;
} else {
func(symbol);
break;
}
}
symbol+=step;
if (!(symbol&step))
{
level++;
step<<=1;
}
}
}
// only works with tree of zeros and ones (and I don't want to specialize this on bool. that would also be ugly)
template <typename F>
void onNotOne(F func)
{
uint32_t step{1U<<(_levels-1)};
uint32_t level{_levels-1};
for (uint32_t symbol=0;symbol<V;)
{
while (_tree[_levelOffsets[level]+(symbol>>level)]!=std::min(step,uint32_t(V)-symbol))
{
if (level)
{
level--;
step>>=1;
} else {
func(symbol);
break;
}
}
symbol+=step;
if (!(symbol&step))
{
level++;
step<<=1;
}
}
}
T operator[](U symbol) const
{
if (symbol>=V)
throw Decompressor::DecompressionError();
return _tree[symbol];
}
void add(U symbol,typename std::make_signed<T>::type freq)
{
if (symbol>=V)
throw Decompressor::DecompressionError();
if (!freq) return;
for (uint32_t i=0;i<_levels;i++)
{
_tree[_levelOffsets[i]+symbol]+=freq;
symbol>>=1;
}
}
void set(U symbol,T freq)
{
if (symbol>=V)
throw Decompressor::DecompressionError();
// TODO: check behavior on large numbers
typename std::make_signed<T>::type delta=freq-_tree[symbol];
add(symbol,delta);
}
T getTotal() const noexcept
{
return _tree[_size-1];
}
private:
static constexpr uint32_t levelSize(uint32_t level)
{
uint32_t ret=V;
for (uint32_t i=0;i<level;i++)
ret=(ret+1)>>1;
return ret;
}
static constexpr uint32_t levels()
{
uint32_t ret{0};
while (levelSize(ret)!=1) ret++;
return ret+1;
}
static constexpr uint32_t size()
{
uint32_t ret{0};
for (uint32_t i=0;i<levels();i++)
ret+=levelSize(i);
return ret;
}
static constexpr uint32_t levelOffset(uint32_t level)
{
uint32_t ret{0};
for (uint32_t i=0;i<level;i++)
ret+=levelSize(i);
return ret;
}
template<uint32_t... I>
static constexpr auto makeLevelOffsetSequence(std::integer_sequence<uint32_t,I...>)
{
return std::integer_sequence<uint32_t,levelOffset(I)...>{};
}
template<uint32_t... I>
static constexpr auto makeLevelSizeSequence(std::integer_sequence<uint32_t,I...>)
{
return std::integer_sequence<uint32_t,levelSize(I)...>{};
}
template<uint32_t... I>
static constexpr std::array<uint32_t,sizeof...(I)> makeArray(std::integer_sequence<uint32_t,I...>)
{
return std::array<uint32_t,sizeof...(I)>{{I...}};
}
static constexpr uint32_t _size{size()};
static constexpr uint32_t _levels{levels()};
static constexpr std::array<uint32_t,_levels> _levelOffsets{makeArray(makeLevelOffsetSequence(std::make_integer_sequence<uint32_t,levels()>{}))};
static constexpr std::array<uint32_t,_levels> _levelSizes{makeArray(makeLevelSizeSequence(std::make_integer_sequence<uint32_t,levels()>{}))};
std::array<T,_size> _tree;
};
}
#endif
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