Add arena debug visualization tool

src/arena_allocator.hpp

@@ -4,6 +4,7 @@
 #include <cstddef>
 #include <cstdint>
 #include <cstdlib>
+#include <cstring>
 #include <iomanip>
 #include <iostream>
 #include <new>
@@ -369,6 +370,181 @@ public:
     return current_block_ ? current_block_->block_count : 0;
   }
 
+  /**
+   * @brief Debug function to find all intra-arena pointers.
+   *
+   * Scans all used memory in the arena for 64-bit aligned values that could be
+   * pointers to locations within the arena itself. This is useful for
+   * understanding memory references and potential data structures.
+   *
+   * @return Vector of PointerInfo structs containing source and target
+   * addresses
+   */
+  struct PointerInfo {
+    const void *source_addr;    ///< Address where the pointer was found
+    size_t source_block_number; ///< Block number containing the source
+    size_t source_offset;       ///< Offset within the source block
+    const void *target_addr;    ///< Address the pointer points to
+    size_t target_block_number; ///< Block number containing the target
+    size_t target_offset;       ///< Offset within the target block
+
+    PointerInfo(const void *src, size_t src_block, size_t src_offset,
+                const void *target, size_t target_block, size_t target_offset)
+        : source_addr(src), source_block_number(src_block),
+          source_offset(src_offset), target_addr(target),
+          target_block_number(target_block), target_offset(target_offset) {}
+  };
+
+  std::vector<PointerInfo> find_intra_arena_pointers() const {
+    std::vector<PointerInfo> pointers;
+
+    if (!current_block_) {
+      return pointers;
+    }
+
+    // Build list of blocks from current to first
+    std::vector<Block *> blocks;
+    Block *block = current_block_;
+    while (block) {
+      blocks.push_back(block);
+      block = block->prev;
+    }
+
+    // Helper function to check if a pointer value points within the used area
+    // of any block
+    auto is_intra_arena_pointer = [&blocks,
+                                   this](uint64_t pointer_value) -> bool {
+      for (size_t block_idx = 0; block_idx < blocks.size(); ++block_idx) {
+        Block *b = blocks[block_idx];
+        uintptr_t block_start = reinterpret_cast<uintptr_t>(b->data());
+
+        // Calculate used bytes in this specific block
+        size_t block_used;
+        if (block_idx == 0) {
+          // Current block - use current_offset_
+          block_used = current_offset_;
+        } else {
+          // Previous blocks are fully used
+          block_used = b->size;
+        }
+
+        uintptr_t block_used_end = block_start + block_used;
+
+        // Check if pointer falls within the used area of this block
+        if (pointer_value >= block_start && pointer_value < block_used_end) {
+          return true;
+        }
+      }
+      return false;
+    };
+
+    // Scan each block for pointers
+    for (size_t block_idx = 0; block_idx < blocks.size(); ++block_idx) {
+      Block *b = blocks[block_idx];
+      const char *data = b->data();
+
+      // Calculate used bytes in this specific block
+      size_t block_used;
+      if (block_idx == 0) {
+        // Current block - use current_offset_
+        block_used = current_offset_;
+      } else {
+        // Previous blocks are fully used
+        block_used = b->size;
+      }
+
+      // Scan for 64-bit aligned pointers
+      for (size_t offset = 0; offset + sizeof(uint64_t) <= block_used;
+           offset += sizeof(uint64_t)) {
+        uint64_t potential_pointer;
+        std::memcpy(&potential_pointer, data + offset,
+                    sizeof(potential_pointer));
+
+        // Check if this value points within the used area of any block
+        if (is_intra_arena_pointer(potential_pointer)) {
+          // Find target location within arena
+          auto target_location = find_address_location(
+              reinterpret_cast<const void *>(potential_pointer));
+
+          pointers.emplace_back(
+              data + offset,             // source address
+              blocks.size() - block_idx, // source block number (1-based)
+              offset,                    // source offset in block
+              reinterpret_cast<const void *>(
+                  potential_pointer), // target address
+              target_location.found ? target_location.block_number
+                                    : 0, // target block number
+              target_location.found ? target_location.offset_in_block
+                                    : 0 // target offset
+          );
+        }
+      }
+    }
+
+    return pointers;
+  }
+
+  /**
+   * @brief Find which block and offset a given address belongs to.
+   *
+   * @param addr The address to locate within the arena
+   * @return PointerInfo with block number and offset, or invalid info if not
+   * found
+   */
+  struct AddressLocation {
+    size_t block_number;
+    size_t offset_in_block;
+    bool found;
+
+    AddressLocation() : block_number(0), offset_in_block(0), found(false) {}
+    AddressLocation(size_t block, size_t offset)
+        : block_number(block), offset_in_block(offset), found(true) {}
+  };
+
+  AddressLocation find_address_location(const void *addr) const {
+    if (!current_block_ || !addr) {
+      return AddressLocation();
+    }
+
+    uintptr_t target_addr = reinterpret_cast<uintptr_t>(addr);
+
+    // Build list of blocks from current to first
+    std::vector<Block *> blocks;
+    Block *block = current_block_;
+    while (block) {
+      blocks.push_back(block);
+      block = block->prev;
+    }
+
+    // Check each block to see if the address falls within its used area
+    for (size_t block_idx = 0; block_idx < blocks.size(); ++block_idx) {
+      Block *b = blocks[block_idx];
+      uintptr_t block_start = reinterpret_cast<uintptr_t>(b->data());
+
+      // Calculate used bytes in this specific block
+      size_t block_used;
+      if (block_idx == 0) {
+        // Current block - use current_offset_
+        block_used = current_offset_;
+      } else {
+        // Previous blocks are fully used
+        block_used = b->size;
+      }
+
+      uintptr_t block_used_end = block_start + block_used;
+
+      // Check if address falls within the used area of this block
+      if (target_addr >= block_start && target_addr < block_used_end) {
+        return AddressLocation(
+            blocks.size() - block_idx, // block number (1-based)
+            target_addr - block_start  // offset within block
+        );
+      }
+    }
+
+    return AddressLocation(); // Not found
+  }
+
   /**
    * @brief Debug function to visualize the arena's layout and contents.
    *