rustdoc-search: better hashing, faster unification

The hash changes are based on some tests with `arti` and various
specific queries, aimed at reducing the false positive rate.

Sorting the query elements so that generics always come first is
instead aimed at reducing the number of Map operations on mgens,
assuming if the bloom filter does find a false positive, it'll
be able to reject the row without having to track a mapping.

src/librustdoc/html/static/js/search.js

@@ -2283,7 +2283,7 @@ function initSearch(rawSearchIndex) {
                 parsedQuery.elems.sort(sortQ);
                 parsedQuery.returned.sort(sortQ);
                 for (i = 0, nSearchWords = searchWords.length; i < nSearchWords; ++i) {
-                    handleArgs(searchIndex[i], i, results_others);
+                    handleArgs(searchIndex[i], searchIndex[i].id, results_others);
                 }
             }
         }
@@ -2847,23 +2847,32 @@ ${item.displayPath}<span class="${type}">${name}</span>\
      * @param {Set<number>} fps - Set of distinct items
      */
     function buildFunctionTypeFingerprint(type, output, fps) {
-
         let input = type.id;
         // All forms of `[]` get collapsed down to one thing in the bloom filter.
         // Differentiating between arrays and slices, if the user asks for it, is
         // still done in the matching algorithm.
         if (input === typeNameIdOfArray || input === typeNameIdOfSlice) {
             input = typeNameIdOfArrayOrSlice;
         }
-        if (input !== null) {
+        const fxScram = k => {
             // https://docs.rs/rustc-hash/1.1.0/src/rustc_hash/lib.rs.html#60
-            // Rotate is skipped because we're only doing one cycle anyway.
-            const h0 = Math.imul(input, 0x9e3779b9);
-            const h1 = Math.imul(479001599 ^ input, 0x9e3779b9);
-            const h2 = Math.imul(433494437 ^ input, 0x9e3779b9);
-            output[0] |= 1 << (h0 % 32);
-            output[1] |= 1 << (h1 % 32);
-            output[2] |= 1 << (h2 % 32);
+            return Math.imul((k << 5) | (k >> 27), 0x9e3779b9);
+        };
+        const murmurScram = k => {
+            // https://en.wikipedia.org/wiki/MurmurHash
+            k = Math.imul(k, 0xcc9e2d51);
+            return Math.imul((k << 15) | (k >> 17), 0x1b873593);
+        };
+        if (input !== null) {
+            const h0a = fxScram(input);
+            const h0b = murmurScram(input);
+            const h1a = fxScram(479001599 ^ input);
+            const h1b = murmurScram(479001599 ^ input);
+            const h2a = fxScram(433494437 ^ input);
+            const h2b = murmurScram(433494437 ^ input);
+            output[0] |= (1 << (h0a % 32)) | (1 << (h0b % 32));
+            output[1] |= (1 << (h1a % 32)) | (1 << (h1b % 32));
+            output[2] |= (1 << (h2a % 32)) | (1 << (h2b % 32));
             fps.add(input);
         }
         for (const g of type.generics) {
@@ -2892,7 +2901,6 @@ ${item.displayPath}<span class="${type}">${name}</span>\
      *                           This function might return 0!
      */
     function compareTypeFingerprints(fullId, queryFingerprint) {
-
         const fh0 = functionTypeFingerprint[fullId * 4];
         const fh1 = functionTypeFingerprint[(fullId * 4) + 1];
         const fh2 = functionTypeFingerprint[(fullId * 4) + 2];