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// Copyright 2012 Google Inc. All Rights Reserved.
//
// This code is licensed under the same terms as WebM:
// Software License Agreement: http://www.webmproject.org/license/software/
// Additional IP Rights Grant: http://www.webmproject.org/license/additional/
// -----------------------------------------------------------------------------
//
// Utilities for building and looking up Huffman trees.
//
// Author: Urvang Joshi (urvang@google.com)
#include <assert.h>
#include <stdlib.h>
#include "./huffman.h"
#include "../utils/utils.h"
#include "webp/format_constants.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
#define NON_EXISTENT_SYMBOL (-1)
static void TreeNodeInit(HuffmanTreeNode* const node) {
node->children_ = -1; // means: 'unassigned so far'
}
static int NodeIsEmpty(const HuffmanTreeNode* const node) {
return (node->children_ < 0);
}
static int IsFull(const HuffmanTree* const tree) {
return (tree->num_nodes_ == tree->max_nodes_);
}
static void AssignChildren(HuffmanTree* const tree,
HuffmanTreeNode* const node) {
HuffmanTreeNode* const children = tree->root_ + tree->num_nodes_;
node->children_ = (int)(children - node);
assert(children - node == (int)(children - node));
tree->num_nodes_ += 2;
TreeNodeInit(children + 0);
TreeNodeInit(children + 1);
}
static int TreeInit(HuffmanTree* const tree, int num_leaves) {
assert(tree != NULL);
if (num_leaves == 0) return 0;
// We allocate maximum possible nodes in the tree at once.
// Note that a Huffman tree is a full binary tree; and in a full binary tree
// with L leaves, the total number of nodes N = 2 * L - 1.
tree->max_nodes_ = 2 * num_leaves - 1;
tree->root_ = (HuffmanTreeNode*)WebPSafeMalloc((uint64_t)tree->max_nodes_,
sizeof(*tree->root_));
if (tree->root_ == NULL) return 0;
TreeNodeInit(tree->root_); // Initialize root.
tree->num_nodes_ = 1;
return 1;
}
void HuffmanTreeRelease(HuffmanTree* const tree) {
if (tree != NULL) {
free(tree->root_);
tree->root_ = NULL;
tree->max_nodes_ = 0;
tree->num_nodes_ = 0;
}
}
int HuffmanCodeLengthsToCodes(const int* const code_lengths,
int code_lengths_size, int* const huff_codes) {
int symbol;
int code_len;
int code_length_hist[MAX_ALLOWED_CODE_LENGTH + 1] = { 0 };
int curr_code;
int next_codes[MAX_ALLOWED_CODE_LENGTH + 1] = { 0 };
int max_code_length = 0;
assert(code_lengths != NULL);
assert(code_lengths_size > 0);
assert(huff_codes != NULL);
// Calculate max code length.
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > max_code_length) {
max_code_length = code_lengths[symbol];
}
}
if (max_code_length > MAX_ALLOWED_CODE_LENGTH) return 0;
// Calculate code length histogram.
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
++code_length_hist[code_lengths[symbol]];
}
code_length_hist[0] = 0;
// Calculate the initial values of 'next_codes' for each code length.
// next_codes[code_len] denotes the code to be assigned to the next symbol
// of code length 'code_len'.
curr_code = 0;
next_codes[0] = -1; // Unused, as code length = 0 implies code doesn't exist.
for (code_len = 1; code_len <= max_code_length; ++code_len) {
curr_code = (curr_code + code_length_hist[code_len - 1]) << 1;
next_codes[code_len] = curr_code;
}
// Get symbols.
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > 0) {
huff_codes[symbol] = next_codes[code_lengths[symbol]]++;
} else {
huff_codes[symbol] = NON_EXISTENT_SYMBOL;
}
}
return 1;
}
static int TreeAddSymbol(HuffmanTree* const tree,
int symbol, int code, int code_length) {
HuffmanTreeNode* node = tree->root_;
const HuffmanTreeNode* const max_node = tree->root_ + tree->max_nodes_;
while (code_length-- > 0) {
if (node >= max_node) {
return 0;
}
if (NodeIsEmpty(node)) {
if (IsFull(tree)) return 0; // error: too many symbols.
AssignChildren(tree, node);
} else if (HuffmanTreeNodeIsLeaf(node)) {
return 0; // leaf is already occupied.
}
node += node->children_ + ((code >> code_length) & 1);
}
if (NodeIsEmpty(node)) {
node->children_ = 0; // turn newly created node into a leaf.
} else if (!HuffmanTreeNodeIsLeaf(node)) {
return 0; // trying to assign a symbol to already used code.
}
node->symbol_ = symbol; // Add symbol in this node.
return 1;
}
int HuffmanTreeBuildImplicit(HuffmanTree* const tree,
const int* const code_lengths,
int code_lengths_size) {
int symbol;
int num_symbols = 0;
int root_symbol = 0;
assert(tree != NULL);
assert(code_lengths != NULL);
// Find out number of symbols and the root symbol.
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > 0) {
// Note: code length = 0 indicates non-existent symbol.
++num_symbols;
root_symbol = symbol;
}
}
// Initialize the tree. Will fail for num_symbols = 0
if (!TreeInit(tree, num_symbols)) return 0;
// Build tree.
if (num_symbols == 1) { // Trivial case.
const int max_symbol = code_lengths_size;
if (root_symbol < 0 || root_symbol >= max_symbol) {
HuffmanTreeRelease(tree);
return 0;
}
return TreeAddSymbol(tree, root_symbol, 0, 0);
} else { // Normal case.
int ok = 0;
// Get Huffman codes from the code lengths.
int* const codes =
(int*)WebPSafeMalloc((uint64_t)code_lengths_size, sizeof(*codes));
if (codes == NULL) goto End;
if (!HuffmanCodeLengthsToCodes(code_lengths, code_lengths_size, codes)) {
goto End;
}
// Add symbols one-by-one.
for (symbol = 0; symbol < code_lengths_size; ++symbol) {
if (code_lengths[symbol] > 0) {
if (!TreeAddSymbol(tree, symbol, codes[symbol], code_lengths[symbol])) {
goto End;
}
}
}
ok = 1;
End:
free(codes);
ok = ok && IsFull(tree);
if (!ok) HuffmanTreeRelease(tree);
return ok;
}
}
int HuffmanTreeBuildExplicit(HuffmanTree* const tree,
const int* const code_lengths,
const int* const codes,
const int* const symbols, int max_symbol,
int num_symbols) {
int ok = 0;
int i;
assert(tree != NULL);
assert(code_lengths != NULL);
assert(codes != NULL);
assert(symbols != NULL);
// Initialize the tree. Will fail if num_symbols = 0.
if (!TreeInit(tree, num_symbols)) return 0;
// Add symbols one-by-one.
for (i = 0; i < num_symbols; ++i) {
if (codes[i] != NON_EXISTENT_SYMBOL) {
if (symbols[i] < 0 || symbols[i] >= max_symbol) {
goto End;
}
if (!TreeAddSymbol(tree, symbols[i], codes[i], code_lengths[i])) {
goto End;
}
}
}
ok = 1;
End:
ok = ok && IsFull(tree);
if (!ok) HuffmanTreeRelease(tree);
return ok;
}
#if defined(__cplusplus) || defined(c_plusplus)
} // extern "C"
#endif