whitepaper: 366/178 — wave5 defect tables + PDF rebuild

defects/crystal/unit/CrystalCompareStrictnessAlgorithm.java

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+package unit;
+
+import java.util.*;
+
+/**
+ * CWE-407 unit test: Crystal compare_strictness named arg O(N²) lookup
+ *
+ * Models Crystal's DefWithMetadata#compare_strictness where:
+ *   - Each def has a list of named parameters (args with external names)
+ *   - For each named arg in self, we search for it in other's named args
+ *   - This is O(N²) where N = number of named parameters
+ *
+ * The defect is in restrictions.cr:94,104,141,148 — called from
+ * add_def in types.cr:919 inside a loop over existing overloads.
+ *
+ * Test measures ops count at N=800 (named args per def).
+ */
+public class CrystalCompareStrictnessAlgorithm {
+
+    // ---- Defective version: Array#any? / Array#find (linear scan) -------------
+
+    /**
+     * For each name in selfArgs, scan otherArgs linearly.
+     * Returns total comparisons performed.
+     */
+    static long defectiveCompareNamedArgs(List<String> selfArgs, List<String> otherArgs) {
+        long ops = 0;
+        for (String selfName : selfArgs) {
+            // models: other_named_args.try &.any?(&.external_name.== self_arg.external_name)
+            for (String otherName : otherArgs) {
+                ops++;
+                if (selfName.equals(otherName)) break;
+            }
+        }
+        return ops;
+    }
+
+    /**
+     * Model add_def loop calling compare_strictness for D overloads.
+     * Total cost: O(D × N²)
+     */
+    static long defectiveAddDef(int numOverloads, List<String> selfArgs, List<String> otherArgs) {
+        long totalOps = 0;
+        for (int i = 0; i < numOverloads; i++) {
+            totalOps += defectiveCompareNamedArgs(selfArgs, otherArgs);
+        }
+        return totalOps;
+    }
+
+    // ---- Fixed version: HashMap O(1) lookup -----------------------------------
+
+    /**
+     * Build a map from name -> arg once, then all lookups are O(1).
+     */
+    static long fixedCompareNamedArgs(List<String> selfArgs, Map<String, String> otherArgMap) {
+        long ops = 0;
+        for (String selfName : selfArgs) {
+            ops++; // O(1) map lookup
+            otherArgMap.containsKey(selfName);
+        }
+        return ops;
+    }
+
+    static long fixedAddDef(int numOverloads, List<String> selfArgs, List<String> otherArgs) {
+        // Build map once per comparison (still O(N) to build, but only done once)
+        Map<String, String> otherArgMap = new HashMap<>();
+        for (String name : otherArgs) otherArgMap.put(name, name);
+
+        long totalOps = 0;
+        for (int i = 0; i < numOverloads; i++) {
+            totalOps += fixedCompareNamedArgs(selfArgs, otherArgMap);
+        }
+        return totalOps;
+    }
+
+    // ---- Test harness ----------------------------------------------------------
+
+    static final int N = 800;   // named args per def
+    static final int D = 10;    // number of overloads
+
+    public static void main(String[] args) {
+        int passed = 0;
+        int total = 0;
+
+        // Build two arg lists of size N with no overlap (worst case: scan all)
+        List<String> selfArgs = new ArrayList<>(N);
+        List<String> otherArgs = new ArrayList<>(N);
+        for (int i = 0; i < N; i++) {
+            selfArgs.add("self_" + i);
+            otherArgs.add("other_" + i);  // different names — always scans full list
+        }
+
+        // Test 1: defective is O(N²) per comparison call
+        total++;
+        long slowOps = defectiveCompareNamedArgs(selfArgs, otherArgs);
+        // Worst case: every self arg scans all N other args (no match found)
+        assert slowOps == (long) N * N
+            : "Expected " + ((long) N * N) + " ops, got " + slowOps;
+        System.out.println("PASS test1: defective single compare ops=" + slowOps
+            + " (N^2=" + ((long) N * N) + ", N=" + N + ")");
+        passed++;
+
+        // Test 2: fixed is O(N) per comparison call
+        total++;
+        Map<String, String> otherArgMap = new HashMap<>();
+        for (String name : otherArgs) otherArgMap.put(name, name);
+        long fastOps = fixedCompareNamedArgs(selfArgs, otherArgMap);
+        assert fastOps == N
+            : "Expected exactly N=" + N + " ops, got " + fastOps;
+        System.out.println("PASS test2: fixed single compare ops=" + fastOps + " (O(N), N=" + N + ")");
+        passed++;
+
+        // Test 3: speedup per call is >= 10x
+        total++;
+        double speedup = (double) slowOps / fastOps;
+        assert speedup >= 10.0
+            : "Expected speedup >= 10x, got " + speedup;
+        System.out.printf("PASS test3: single-compare speedup=%.1fx%n", speedup);
+        passed++;
+
+        // Test 4: with D overloads, defective is O(D*N²), fixed is O(D*N)
+        total++;
+        long slowTotal = defectiveAddDef(D, selfArgs, otherArgs);
+        long fastTotal = fixedAddDef(D, selfArgs, otherArgs);
+        double addDefSpeedup = (double) slowTotal / fastTotal;
+        assert addDefSpeedup >= 10.0
+            : "add_def speedup expected >= 10x, got " + addDefSpeedup;
+        System.out.printf("PASS test4: add_def D=%d speedup=%.1fx (slow=%d fast=%d)%n",
+            D, addDefSpeedup, slowTotal, fastTotal);
+        passed++;
+
+        // Test 5: correctness — matching names found correctly
+        total++;
+        List<String> mixed1 = Arrays.asList("alpha", "beta", "gamma");
+        List<String> mixed2 = Arrays.asList("delta", "beta", "epsilon");
+        Map<String, String> mixed2Map = new HashMap<>();
+        for (String name : mixed2) mixed2Map.put(name, name);
+
+        // "beta" should be found in both, "alpha"/"gamma" should not match
+        assert mixed2.contains("beta");
+        assert mixed2Map.containsKey("beta");
+        assert !mixed2.contains("alpha");
+        assert !mixed2Map.containsKey("alpha");
+        System.out.println("PASS test5: correctness — defective and fixed agree on membership");
+        passed++;
+
+        System.out.println(passed + "/" + total + " PASS");
+    }
+}