Added iterative decoder; fixed bit alignments

pull/1/head
Clyne 4 years ago committed by GitHub
parent 40fc0b29f5
commit 70bb15bd3c
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GPG Key ID: 4AEE18F83AFDEB23

@ -55,7 +55,7 @@ private:
auto end = node_count();
size_t endend = 255;
unsigned char endv = 0xFF;
unsigned char endv = 0xFE;
while (table[1].freq != 0) {
node n { endv--,
table[0].freq + table[1].freq,
@ -103,9 +103,10 @@ private:
// Returns a pair: [total byte size, bits used in last byte].
consteval static auto output_size() {
auto tree = build_node_tree();
size_t bytes = 0, bits = 0;
size_t bytes = 1, bits = 0;
for (size_t i = 0; i < std::char_traits<char>::length(data); i++) {
auto leaf = std::find_if(tree.begin(), tree.end(), [c = data[i]](auto& n) { return n.value == c; });
auto leaf = std::find_if(tree.begin(), tree.end(),
[c = data[i]](auto& n) { return n.value == c; });
while (leaf->parent != -1) {
if (++bits == 8)
bits = 0, bytes++;
@ -114,27 +115,23 @@ private:
}
delete[] tree.data();
return std::make_pair(bytes + 1, bits);
return std::make_pair(bytes, bits);
}
// Compresses the input data, placing the result in `output`.
consteval void compress()
{
auto tree = build_node_tree();
size_t bytes = size();
int bits = 5;
int bits = 8 - output_size().second;
for (size_t i = std::char_traits<char>::length(data); i > 0; i--) {
auto leaf = std::find_if(tree.begin(), tree.begin() + tree_count(), [c = data[i - 1]](auto& n) { return n.value == c; });
auto leaf = std::find_if(tree.begin(), tree.begin() + tree_count(),
[c = data[i - 1]](auto& n) { return n.value == c; });
while (leaf->parent != -1) {
auto parent = tree.begin() + leaf->parent;
if (parent->right == leaf->value)
output[bytes - 1] |= (1 << bits);
if (++bits == 8) {
bits = 0;
if (--bytes == 0) {
i = 1;
break;
}
}
if (++bits == 8)
bits = 0, --bytes;
leaf = parent;
}
}
@ -143,10 +140,21 @@ private:
// Builds the tree that can be used for decompression, stored in `decode_tree`.
consteval void build_decode_tree() {
auto tree = build_node_tree();
for (size_t i = 0; i < tree_count(); i++) {
decode_tree[i] = tree[i].value;
decode_tree[i + 1] = std::max(tree[i].left, 0);
decode_tree[i + 1] = std::max(tree[i].right, 0);
decode_tree[i * 3] = tree[i].value;
size_t j;
for (j = i + 1; j < tree_count(); j++) {
if (tree[i].left == tree[j].value)
break;
}
decode_tree[i * 3 + 1] = j < tree_count() ? j : 0;
for (j = i + 1; j < tree_count(); j++) {
if (tree[i].right == tree[j].value)
break;
}
decode_tree[i * 3 + 2] = j < tree_count() ? j : 0;
}
delete[] tree.data();
}
@ -166,6 +174,48 @@ public:
build_decode_tree();
compress();
}
// Utility for decoding compressed data.
class decode_info {
public:
decode_info(const huffman_compress<data>& data_) :
m_data(data_) { get_next(); }
// Checks if another byte is available
operator bool() const {
return m_pos < (m_data.size() - 1) || m_bit >= (8 - m_data.lastbitscount());
}
// Gets the current byte
int operator*() const { return m_current; }
// Moves to the next byte
int operator++() {
get_next();
return m_current;
}
private:
// Internal: moves to next byte
void get_next() {
auto node = m_data.decode_tree;
do {
bool bit = m_data.output[m_pos] & (1 << (m_bit - 1));
if (--m_bit == 0)
m_bit = 8, m_pos++;
node = m_data.decode_tree + 3 * node[bit ? 2 : 1];
} while (node[1] != 0);
m_current = *node;
}
const huffman_compress<data>& m_data;
size_t m_pos = 0;
unsigned char m_bit = 8;
int m_current = -1;
};
// Creates a decoder object for iteratively decompressing the data.
auto get_decoder() const {
return decode_info(*this);
}
};
#endif // TCSULLIVAN_CONSTEVAL_HUFFMAN_HPP_

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