clyne/consteval-huffman
1
0
Fork 0
Code Issues 3 Pull Requests Projects Releases Wiki Activity

prevent compression if it doesn't save space

Browse Source
This commit is contained in:
Clyne 2020-11-15 18:55:40 -05:00 committed by GitHub
parent e58cd38132
commit 2fbe5393df
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 41 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

70
consteval_huffman.hpp
View File

@ -1,4 +1,3 @@
/**
* consteval_huffman.hpp - Provides compile-time text compression.
* Written by Clyne Sullivan.
@ -216,12 +215,18 @@ private:
delete[] tree.data();
}
// Contains the compressed data.
unsigned char compressed_data[compressed_size_info().first] = {};
// Contains a 'tree' that can be used to decompress the data.
unsigned char decode_tree[3 * tree_count()] = {};
public:
consteval static auto compressed_size() {
return compressed_size_info().first + 3 * tree_count();
}
consteval static auto uncompressed_size() {
return data_length;
}
consteval static size_t bytes_saved() {
size_t diff = uncompressed_size() - compressed_size();
return diff > 0 ? diff : 0;
}
// Utility for decoding compressed data.
class decode_info {
public:
@ -230,8 +235,12 @@ public:
// Checks if another byte is available
operator bool() const {
const auto [size_bytes, last_bits] = m_data.compressed_size_info();
return m_pos < (size_bytes - 1) || m_bit > (8 - last_bits);
if constexpr (bytes_saved() > 0) {
const auto [size_bytes, last_bits] = m_data.compressed_size_info();
return m_pos < (size_bytes - 1) || m_bit > (8 - last_bits);
} else {
return m_pos < data_length;
}
}
// Gets the current byte
@ -245,14 +254,18 @@ public:
private:
// Internal: moves to next byte
void get_next() {
auto *node = m_data.decode_tree;
do {
bool bit = m_data.compressed_data[m_pos] & (1 << (m_bit - 1));
if (--m_bit == 0)
m_bit = 8, m_pos++;
node += 3 * node[bit ? 2 : 1];
} while (node[1] != 0);
m_current = *node;
if constexpr (bytes_saved() > 0) {
auto *node = m_data.decode_tree;
do {
bool bit = m_data.compressed_data[m_pos] & (1 << (m_bit - 1));
if (--m_bit == 0)
m_bit = 8, m_pos++;
node += 3 * node[bit ? 2 : 1];
} while (node[1] != 0);
m_current = *node;
} else {
m_current = data[m_pos++];
}
}
const huffman_compress<data>& m_data;
@ -264,25 +277,24 @@ public:
};
consteval huffman_compress() {
build_decode_tree();
compress();
}
consteval static auto compressed_size() {
return sizeof(compressed_data) + sizeof(decode_tree);
}
consteval static auto uncompressed_size() {
return data_length;
}
consteval static size_t bytes_saved() {
return uncompressed_size() - compressed_size();
if constexpr (bytes_saved() > 0) {
build_decode_tree();
compress();
} else {
std::copy(data, data + data_length, compressed_data);
}
}
// Creates a decoder object for iteratively decompressing the data.
auto get_decoder() const {
return decode_info(*this);
}
private:
// Contains the compressed data.
unsigned char compressed_data[bytes_saved() > 0 ? compressed_size_info().first : data_length] = {};
// Contains a 'tree' that can be used to decompress the data.
unsigned char decode_tree[3 * tree_count()] = {};
};
#endif // TCSULLIVAN_CONSTEVAL_HUFFMAN_HPP_