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consteval-huffman
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Add data(); optimize decoder

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Clyne 4 years ago committed by GitHub
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1 changed files with 46 additions and 33 deletions
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consteval_huffman.hpp
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@ -8,7 +8,9 @@
#define TCSULLIVAN_CONSTEVAL_HUFFMAN_HPP_
#include <algorithm>
#include <concepts>
#include <span>
#include <type_traits>
namespace detail
{
@ -35,11 +37,11 @@ namespace detail
* minimal run-time interface for decompressing the data.
* @tparam data The string of data to be compressed.
*/
template<auto data>
template<auto raw_data>
requires(
std::same_as<decltype(data),
const detail::huffman_string_container<data.size()>> &&
data.size() > 0)
std::same_as<std::remove_cvref_t<decltype(raw_data)>,
detail::huffman_string_container<raw_data.size()>> &&
raw_data.size() > 0)
class huffman_compressor
{
using size_t = long int;
@ -69,8 +71,8 @@ private:
auto list = std::span(new node[256] {}, 256);
for (int i = 0; i < 256; i++)
list[i].value = i;
for (usize_t i = 0; i < data.size(); i++)
list[data[i]].freq++;
for (usize_t i = 0; i < raw_data.size(); i++)
list[raw_data[i]].freq++;
std::sort(list.begin(), list.end(),
[](const auto& a, const auto& b) { return a.freq < b.freq; });
@ -164,9 +166,9 @@ private:
auto tree = build_node_tree();
size_t bytes = 1, bits = 0;
for (usize_t i = 0; i < data.size(); i++) {
for (usize_t i = 0; i < raw_data.size(); i++) {
auto leaf = std::find_if(tree.begin(), tree.end(),
[c = data[i]](const auto& n) { return n.value == c; });
[c = raw_data[i]](const auto& n) { return n.value == c; });
while (leaf->parent != -1) {
if (++bits == 8)
@ -194,9 +196,9 @@ private:
// Compress data backwards, because we obtain the Huffman codes backwards
// as we traverse towards the parent node.
for (auto i = data.size(); i > 0; i--) {
for (auto i = raw_data.size(); i > 0; i--) {
auto leaf = std::find_if(tree.begin(), tree.end(),
[c = data[i - 1]](auto& n) { return n.value == c; });
[c = raw_data[i - 1]](auto& n) { return n.value == c; });
while (leaf->parent != -1) {
auto parent = tree.begin() + leaf->parent;
@ -218,6 +220,7 @@ private:
*/
consteval void build_decode_tree() noexcept {
auto tree = build_node_tree();
auto decode_tree = compressed_data + compressed_size_info().first;
for (usize_t i = 0; i < tree_count(); i++) {
// Only store node value if it represents a data value
@ -246,7 +249,7 @@ public:
return compressed_size_info().first + 3 * tree_count();
}
consteval static auto uncompressed_size() noexcept {
return data.size();
return raw_data.size();
}
consteval static size_t bytes_saved() noexcept {
size_t diff = uncompressed_size() - compressed_size();
@ -259,25 +262,27 @@ public:
using difference_type = std::ptrdiff_t;
using value_type = int;
decode_info(const huffman_compressor<data>* comp_data) noexcept
: m_data(comp_data) { get_next(); }
decode_info(const unsigned char *comp_data) noexcept
: m_data(comp_data),
m_table(comp_data + compressed_size_info().first) { get_next(); }
decode_info() = default;
consteval static decode_info end() noexcept {
constexpr static decode_info end(const unsigned char *comp_data) noexcept {
decode_info ender;
ender.m_data = comp_data;
if constexpr (bytes_saved() > 0) {
const auto [size_bytes, last_bits] = compressed_size_info();
ender.m_pos = size_bytes - 1;
ender.m_data += size_bytes - 1;
ender.m_bit = 1 << (7 - last_bits);
} else {
ender.m_pos = data.size() + 1;
ender.m_data += raw_data.size() + 1;
}
return ender;
}
bool operator==(const decode_info& other) const noexcept {
return m_bit == other.m_bit && m_pos == other.m_pos;
return m_data == other.m_data && m_bit == other.m_bit;
}
auto operator*() const noexcept {
return m_current;
@ -294,29 +299,27 @@ public:
private:
void get_next() noexcept {
if (*this == end())
if (*this == end(m_data))
return;
if constexpr (bytes_saved() > 0) {
auto *node = m_data->decode_tree;
auto pos = m_pos;
auto *node = m_table;
int data = *m_data;
auto bit = m_bit;
do {
auto idx = (m_data->compressed_data[pos] & bit) ? 2u : 1u;
node += node[idx] * 3u;
node += (data & bit) ? node[2] * 3u : node[1] * 3u;
bit >>= 1;
if (!bit)
bit = 0x80, pos++;
bit = 0x80, data = *++m_data;
} while (node[1] != 0);
m_pos = pos;
m_bit = bit;
m_current = *node;
} else {
m_current = data[m_pos++];
m_current = *m_data++;
}
}
const huffman_compressor<data> *m_data = nullptr;
size_t m_pos = 0;
const unsigned char *m_data = nullptr;
const unsigned char *m_table = nullptr;
unsigned char m_bit = 0x80;
int m_current = -1;
@ -330,18 +333,28 @@ public:
if constexpr (bytes_saved() > 0) {
build_decode_tree();
compress();
} else {
std::copy(raw_data.data, raw_data.data + raw_data.size(), compressed_data);
}
}
auto begin() const noexcept {
return decode_info(this);
return decode_info(compressed_data);
}
auto end() const noexcept {
return decode_info::end();
return decode_info::end(compressed_data);
}
auto cbegin() const noexcept { begin(); }
auto cend() const noexcept { end(); }
// For accessing the compressed data
auto data() const noexcept {
if constexpr (bytes_saved() > 0)
return compressed_data;
else
return raw_data;
}
auto size() const noexcept {
if constexpr (bytes_saved() > 0)
return compressed_size();
@ -350,10 +363,10 @@ public:
}
private:
// Contains the compressed data.
unsigned char compressed_data[bytes_saved() > 0 ? compressed_size_info().first : 1] = {0};
// Contains a 'tree' that can be used to decompress the data.
unsigned char decode_tree[bytes_saved() > 0 ? 3 * tree_count() : 1] = {0};
// Contains the compressed data, followed by the decoding tree.
unsigned char compressed_data[
bytes_saved() > 0 ? compressed_size_info().first + 3 * tree_count()
: raw_data.size()] = {0};
};
template <detail::huffman_string_container hsc>

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