fix(hamt): shrink root pointer by 8 bytes

build.zig

@@ -37,6 +37,7 @@ pub fn build(b: *std.Build) void {
         .root_source_file = b.path("src/bench.zig"),
         .target = target,
         .optimize = .ReleaseFast,
+        .link_libc = true,
     });
     bench.root_module.addImport("hamt", mod);
 

src/bench.zig

@@ -2,10 +2,10 @@ const std = @import("std");
 const HashArrayMappedTrie = @import("hamt").HashArrayMappedTrie;
 
 const StringContext = struct {
-    pub const Digest = u64;
+    pub const Digest = u32;
 
     pub fn hash(input: []const u8) Digest {
-        return std.hash.Wyhash.hash(0, input);
+        return @truncate(std.hash.Wyhash.hash(0, input));
     }
 
     pub fn eql(left: []const u8, right: []const u8) bool {
@@ -17,16 +17,13 @@ const StringArrayHashMap = std.array_hash_map.StringArrayHashMap(void);
 const StringHashMap = std.hash_map.StringHashMap(void);
 
 pub fn main() !void {
-    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    const allocator = std.heap.c_allocator;
-    defer std.debug.assert(gpa.deinit() == .ok);
-
-    const allocator = gpa.allocator();
     const elem_count = 1000;
 
     const keys = try allocator.alloc([32]u8, elem_count);
     defer allocator.free(keys);
 
-    var rand = std.rand.DefaultPrng.init(1337);
+    var rand = std.rand.DefaultPrng.init(0);
     for (keys) |*key| rand.fill(key);
 
     var trie = try HashArrayMappedTrie([]const u8, void, StringContext).init(allocator);

src/trie.zig

@@ -18,7 +18,7 @@ pub fn HashArrayMappedTrie(comptime K: type, comptime V: type, comptime Context:
         const t: Log2Int(Digest) = @intCast(@typeInfo(Log2Int(Digest)).Int.bits);
 
         free_list: FreeList,
-        root: []?*Node,
+        root: *[table_size]?*Node,
 
         const Node = union(enum) { kv: Pair, table: Table };
         const Table = struct { map: Digest = 0, base: [*]Node };
@@ -146,7 +146,7 @@ pub fn HashArrayMappedTrie(comptime K: type, comptime V: type, comptime Context:
 
         pub fn init(allocator: Allocator) !Self {
             // TODO: Add ability to have a larger root node (for quicker lookup times)
-            const root = try allocator.alloc(?*Node, table_size);
+            const root = try allocator.create([table_size]?*Node);
             @memset(root, null);
 
             return Self{ .root = root, .free_list = try FreeList.init(allocator) };
@@ -181,7 +181,7 @@ pub fn HashArrayMappedTrie(comptime K: type, comptime V: type, comptime Context:
             }
         }
 
-        fn tableIdx(hash: Digest, offset: u16) Log2Int(Digest) {
+        inline fn tableIdx(hash: Digest, offset: u16) Log2Int(Digest) {
             const shift_amt: Log2Int(Digest) = @intCast(table_size - offset);
 
             return @truncate(hash >> shift_amt);
@@ -198,13 +198,12 @@ pub fn HashArrayMappedTrie(comptime K: type, comptime V: type, comptime Context:
                 switch (current.*) {
                     .table => |table| {
                         const mask = @as(Digest, 1) << tableIdx(hash, hash_offset);
+                        if (table.map & mask == 0) return null; // empty table
 
-                        if (table.map & mask != 0) {
+                        const idx = @popCount(table.map & (mask - 1));
-                            const idx = @popCount(table.map & (mask - 1));
+                        current = &table.base[idx];
-                            current = &table.base[idx];
 
-                            hash_offset += t;
+                        hash_offset += t;
-                        } else return null; // hash table entry is empty
                     },
                     .kv => |pair| {
                         if (!Context.eql(pair.key, key)) return null;