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reach: binary_heap bug fixes #42

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4df35ee
binary_heap bug fixes
abagnall-riverside Dec 5, 2025
24bb206
Remove redundant argparse argument
abagnall-riverside Dec 5, 2025
79b33ad
Add ascii illustration of 0-indexing structure
abagnall-riverside Dec 5, 2025
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3 changes: 0 additions & 3 deletions reach/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -85,9 +85,6 @@ stdout if no path was given.
Under `lib/`:
- json.hpp
+ open-source (MIT) JSON library from https://github.com/nlohmann/json
- cache.hpp
+ templated helper functions for reading/writing data structures
(vector, unordered_set, unordered_map) to/from disk
- facts.hpp, facts.cpp
+ in-memory representation of fact databases, and loading from .facts files
+ defns related to dlsym loaded symbol logs from dynamic analysis
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17 changes: 12 additions & 5 deletions reach/lib/binary_heap.hpp
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Expand Up @@ -31,11 +31,18 @@ class binary_heap {

// Extract the minimum element from the heap.
std::pair<K, V> extract() {
if (_heap.empty()) {
throw std::out_of_range("extract on empty heap");
}
const auto root = this->_heap.front();
this->_heap[0] = this->_heap.back();
this->_heap.pop_back();
this->_ixs.erase(root.first);
if (this->_heap.size() == 1) {
this->_heap.pop_back();
return root;
}
this->_heap[0] = this->_heap.back();
this->_ixs[this->_heap[0].first] = 0;
this->_heap.pop_back();
this->_heapify_down(0);
return root;
}
Expand Down Expand Up @@ -69,7 +76,7 @@ class binary_heap {
// Heapify up at index [i].
void _heapify_up(size_t i) {
if (i > 0) {
size_t parent_i = i / 2;
size_t parent_i = (i - 1) / 2;
if (this->_heap[i].second < this->_heap[parent_i].second) {
this->_swap(i, parent_i);
this->_heapify_up(parent_i);
Expand All @@ -79,8 +86,8 @@ class binary_heap {

// Heapify down at index [i].
void _heapify_down(size_t i) {
size_t left_i = 2 * i;
size_t right_i = 2 * i + 1;
size_t left_i = 2 * i + 1;
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@srosefield-riverside srosefield-riverside Dec 5, 2025

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Add a comment here to explain the indexing structure? I'm fond of ascii art so a graph like this makes sense to me, but choose what you feel is best.

       0
   1       2
 3   4   5    6

Is it supposed to be index i is at i and its children are at 2i +1, 2i+2? I guess this is the result of 0-indexing instead of 1-indexing as the old version would have worked before.

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@abagnall-riverside abagnall-riverside Dec 5, 2025

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Added to the top of the file. Honestly, I would rather avoid using a custom binary heap implementation. I just threw this in because I had it lying around.

size_t right_i = 2 * i + 2;

size_t smallest = i;
if (left_i < this->_heap.size() &&
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2 changes: 0 additions & 2 deletions reach/src/main.cpp
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Expand Up @@ -132,8 +132,6 @@ int main(int argc, char* argv[]) {
.flag();
program.add_argument("-ds", "--dlsym-log")
.help("path to file containing dlsym log of loaded symbols");
program.add_argument("-o", "--output")
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@srosefield-riverside srosefield-riverside Dec 5, 2025

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Why was this argument removed? Fairly certain it is still used.

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@abagnall-riverside abagnall-riverside Dec 5, 2025

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It's still there. This removed the second redundant call to add_argument for the --output argument.

.help("JSON output path");
program.add_argument("-g", "--graph")
.help("graph type (\"simple\", \"cfg\", or \"call\"). Default \"cfg\"");
program.add_argument("-n", "--num-paths")
Expand Down