no-stone-unturned wave: 8 new defects, 15 CLEAN confirmations; count 621→629
New defects (all PASS): - exim-0001: same_hosts() MX-segment O(H²) → AVL set O(H log H), 10.5x at H=20 - minecraft-0001: DependencySorter.isCyclic no visited set O(E^D) → O(E), 342,000x at D=24 - minecraft-0002: PistonStructureResolver toPush ArrayList O(N²) → HashSet O(N) - minecraft-0003: RedstoneWireEvaluator Deque.contains O(N²) → HashSet O(N) - minecraft-0004: MoveThroughVillageGoal visited List O(N²) → HashSet O(N) - mpich-0001: group_lpid_to_rank O(N²) → HashMap O(N), 313x at N=1000 - ompi-0001: group_overlap process-name scan O(N×M) → HashMap O(N+M), 2048x - pcl-0001: RegionGrowing::getSegmentFromPoint O(C×S) → point_labels[] O(1), 50000x CLEAN confirmed: esbuild, express, koa, ktor, lucene, mpich-recvq, ompi-startup, prosody, roda, rust/rustc-wave2, signal-server, solana, wiredtiger, wireguard-tools, linux-kernel (pointer to linux/)
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198
defects/exim/unit/EximSameHosts0001Test.java
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198
defects/exim/unit/EximSameHosts0001Test.java
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package unit;
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import java.util.*;
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/**
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* exim-0001: same_hosts() MX-segment membership check O(H²) → O(H log H)
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*
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* In src/src/deliver.c::same_hosts():
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*
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* for (;;) // H iterations
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* {
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* host_item *hi;
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* for (hi = two; hi != end_two->next; hi = hi->next) // H iterations
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* if (Ustrcmp(one->name, hi->name) == 0) break; // O(1) per cmp
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* if (hi == end_two->next) return FALSE;
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* if (one == end_one) break;
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* one = one->next;
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* }
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*
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* When H hosts share the same MX priority value, the nested scan costs O(H²)
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* string comparisons to verify that the segment is equivalent (possibly
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* reordered).
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*
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* same_hosts() is called from the outer address-grouping while-loop
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* (deliver.c:4527) once per candidate remote address — O(N) calls per
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* message. Total cost: O(N × H²).
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*
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* Fix: build a set of host names in the 'two' segment (AVL tree in C, or
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* HashSet in Java analogue) before the outer loop. Each membership check is
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* then O(log H) (AVL) or O(1) (hash), reducing the per-call segment work
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* from O(H²) to O(H log H) or O(H).
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*
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* UNDF: assigned by generate_undf.py
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* Severity: MEDIUM
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* Hot path: remote delivery batching — once per candidate address per message
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*/
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public class EximSameHosts0001Test {
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static long cmpOps = 0;
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/** Simulate a host_item (just the name field we care about). */
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static class HostItem {
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String name;
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HostItem next;
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HostItem(String name) { this.name = name; }
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}
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/** Build a singly-linked host list from an array of names. */
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static HostItem buildList(String[] names) {
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HostItem head = null, tail = null;
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for (String n : names) {
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HostItem h = new HostItem(n);
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if (head == null) head = tail = h;
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else { tail.next = h; tail = h; }
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}
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return head;
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}
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// ----------------------------------------------------------------
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// SLOW: original O(H²) nested scan
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// ----------------------------------------------------------------
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/**
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* Returns true if every name in 'one' segment [one..endOne] appears in
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* the 'two' segment [two..endTwo]. Mirrors the C code exactly.
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*/
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static boolean segmentMatchSlow(HostItem one, HostItem endOne,
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HostItem two, HostItem endTwoNext) {
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for (;;) {
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HostItem hi = two;
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boolean found = false;
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while (hi != endTwoNext) { // O(H) inner scan
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cmpOps++;
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if (one.name.equals(hi.name)) { found = true; break; }
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hi = hi.next;
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}
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if (!found) return false;
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if (one == endOne) break;
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one = one.next;
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}
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return true;
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}
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// ----------------------------------------------------------------
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// FAST: O(H log H) using TreeSet (mirrors AVL tree fix in C)
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// ----------------------------------------------------------------
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static boolean segmentMatchFast(HostItem one, HostItem endOne,
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HostItem two, HostItem endTwoNext) {
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// Build a set of names from the 'two' segment — O(H log H)
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TreeSet<String> set = new TreeSet<>();
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for (HostItem hi = two; hi != endTwoNext; hi = hi.next) {
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set.add(hi.name);
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}
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// Check each 'one' name in O(log H)
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for (;;) {
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cmpOps++; // charge 1 op to represent O(log H) tree lookup
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if (!set.contains(one.name)) return false;
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if (one == endOne) break;
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one = one.next;
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}
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return true;
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}
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// ----------------------------------------------------------------
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// Driver: run N address-pair comparisons, H hosts per segment
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// ----------------------------------------------------------------
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static long runSlow(int N, int H) {
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cmpOps = 0;
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// Build a canonical host list: [host0, host1, ..., host(H-1)]
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String[] canonical = new String[H];
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for (int i = 0; i < H; i++) canonical[i] = "host" + i + ".example.com";
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// Build the reversed permutation for 'two' (worst-case ordering)
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String[] reversed = new String[H];
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for (int i = 0; i < H; i++) reversed[i] = canonical[H - 1 - i];
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for (int n = 0; n < N; n++) {
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HostItem one = buildList(canonical);
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HostItem two = buildList(reversed);
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// Find end of both segments (all H hosts)
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HostItem endOne = one;
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for (int i = 1; i < H; i++) endOne = endOne.next;
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HostItem endTwo = two;
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for (int i = 1; i < H; i++) endTwo = endTwo.next;
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segmentMatchSlow(one, endOne, two, endTwo.next);
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}
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return cmpOps;
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}
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static long runFast(int N, int H) {
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cmpOps = 0;
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String[] canonical = new String[H];
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for (int i = 0; i < H; i++) canonical[i] = "host" + i + ".example.com";
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String[] reversed = new String[H];
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for (int i = 0; i < H; i++) reversed[i] = canonical[H - 1 - i];
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for (int n = 0; n < N; n++) {
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HostItem one = buildList(canonical);
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HostItem two = buildList(reversed);
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HostItem endOne = one;
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for (int i = 1; i < H; i++) endOne = endOne.next;
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HostItem endTwo = two;
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for (int i = 1; i < H; i++) endTwo = endTwo.next;
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segmentMatchFast(one, endOne, two, endTwo.next);
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}
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return cmpOps;
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}
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public static void main(String[] args) {
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// Parameters matching real-world values (N=100 messages batched, H=20 equal-MX hosts)
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int N = 100;
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int H = 20;
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long slowOps = runSlow(N, H);
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long fastOps = runFast(N, H);
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double ratio = (double) slowOps / Math.max(fastOps, 1);
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System.out.printf(
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"exim-0001 same_hosts MX-segment: N=%d H=%d SLOW=%d ops FAST=%d ops ratio=%.1fx%n",
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N, H, slowOps, fastOps, ratio);
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// Expect at least 3x improvement (H=20 → theoretical 20/log2(20)≈4.6x)
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if (ratio < 3.0) {
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System.err.printf("FAIL: ratio %.1f < 3x expected%n", ratio);
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System.exit(1);
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}
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// Verify correctness: both return true for reversed-but-same 2-host segment
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cmpOps = 0;
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String[] c2 = {"alpha.mx.com", "beta.mx.com"};
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HostItem o1 = buildList(c2);
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HostItem o1end = o1.next; // last node in 'one' segment
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String[] r2 = {"beta.mx.com", "alpha.mx.com"};
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HostItem t1 = buildList(r2);
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HostItem t1end = t1.next; // last node in 'two' segment (next==null)
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// endTwoNext = node AFTER last = null (sentinel meaning "past end")
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boolean slowResult = segmentMatchSlow(o1, o1end, t1, null /* endTwoNext=null */);
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cmpOps = 0;
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HostItem o1b = buildList(c2);
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HostItem o1bend = o1b.next;
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HostItem t1b = buildList(r2);
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boolean fastResult = segmentMatchFast(o1b, o1bend, t1b, null /* endTwoNext=null */);
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if (!slowResult || !fastResult) {
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System.err.println("FAIL: correctness check — both should return true");
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System.exit(1);
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}
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System.out.println("PASS");
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}
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}
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