chore: initial commit
This commit is contained in:
commit
5e630120f2
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zig-cache/
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zig-out/
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.vscode/
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const std = @import("std");
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// Although this function looks imperative, note that its job is to
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// declaratively construct a build graph that will be executed by an external
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// runner.
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pub fn build(b: *std.Build) void {
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// Standard target options allows the person running `zig build` to choose
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// what target to build for. Here we do not override the defaults, which
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// means any target is allowed, and the default is native. Other options
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// for restricting supported target set are available.
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const target = b.standardTargetOptions(.{});
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// Standard optimization options allow the person running `zig build` to select
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// between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
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// set a preferred release mode, allowing the user to decide how to optimize.
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const optimize = b.standardOptimizeOption(.{});
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const exe = b.addExecutable(.{
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.name = "trie",
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// In this case the main source file is merely a path, however, in more
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// complicated build scripts, this could be a generated file.
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.root_source_file = .{ .path = "src/main.zig" },
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.target = target,
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.optimize = optimize,
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});
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// This declares intent for the executable to be installed into the
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// standard location when the user invokes the "install" step (the default
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// step when running `zig build`).
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exe.install();
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// This *creates* a RunStep in the build graph, to be executed when another
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// step is evaluated that depends on it. The next line below will establish
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// such a dependency.
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const run_cmd = exe.run();
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// By making the run step depend on the install step, it will be run from the
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// installation directory rather than directly from within the cache directory.
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// This is not necessary, however, if the application depends on other installed
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// files, this ensures they will be present and in the expected location.
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run_cmd.step.dependOn(b.getInstallStep());
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// This allows the user to pass arguments to the application in the build
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// command itself, like this: `zig build run -- arg1 arg2 etc`
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if (b.args) |args| {
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run_cmd.addArgs(args);
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}
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// This creates a build step. It will be visible in the `zig build --help` menu,
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// and can be selected like this: `zig build run`
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// This will evaluate the `run` step rather than the default, which is "install".
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const run_step = b.step("run", "Run the app");
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run_step.dependOn(&run_cmd.step);
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// Creates a step for unit testing.
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const exe_tests = b.addTest(.{
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.root_source_file = .{ .path = "src/tests.zig" },
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.target = target,
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.optimize = optimize,
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});
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// Similar to creating the run step earlier, this exposes a `test` step to
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// the `zig build --help` menu, providing a way for the user to request
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// running the unit tests.
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const test_step = b.step("test", "Run unit tests");
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test_step.dependOn(&exe_tests.step);
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}
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//! Hash Array Mapped Trie
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//! https://idea.popcount.org/2012-07-25-introduction-to-hamt/
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const std = @import("std");
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// const Token = @import("Token.zig");
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const Allocator = std.mem.Allocator;
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const HashArrayMappedTrie = @This();
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const t = 5;
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const table_size = std.math.powi(u32, 2, t) catch unreachable;
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root: [table_size]?*Node,
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allocator: Allocator,
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const Node = union(enum) { kv: Pair, table: Table };
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const Pair = struct { key: []const u8, value: void };
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const Table = struct { map: u32 = 0, base: [*]Node };
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pub fn init(allocator: Allocator) !HashArrayMappedTrie {
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return .{
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.root = [_]?*Node{null} ** table_size,
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.allocator = allocator,
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};
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}
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pub fn deinit(self: *HashArrayMappedTrie) void {
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for (self.root) |node| {
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if (node == null) continue;
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deinitRecurse(self.allocator, node.?);
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}
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}
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fn deinitRecurse(allocator: Allocator, node: *Node) void {
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switch (node.*) {
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.kv => allocator.destroy(node),
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else => {},
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}
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}
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fn amtIdx(comptime T: type, bitset: T, offset: u16) std.math.Log2Int(T) {
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const L2I = std.math.Log2Int(T);
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const shift_amt = @intCast(L2I, @typeInfo(T).Int.bits - offset);
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return @truncate(L2I, bitset >> shift_amt);
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}
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pub fn search(self: *HashArrayMappedTrie, key: []const u8) ?Pair {
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const bitset = hash(key);
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// most siginificant t bits from hash
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var hash_offset: u5 = t;
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var current: *Node = self.root[amtIdx(u32, bitset, hash_offset)] orelse return null;
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while (true) {
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switch (current.*) {
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.table => |table| {
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hash_offset += t;
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const mask = @as(u32, 1) << amtIdx(u32, bitset, hash_offset);
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if (table.map & mask != 0) {
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const idx = @popCount(table.map & (mask - 1));
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current = &table.base[idx];
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} else return null; // hash table entry is empty
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},
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.kv => |pair| {
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if (!std.mem.eql(u8, pair.key, key)) return null;
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return pair;
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},
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}
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}
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}
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pub fn insert(self: *HashArrayMappedTrie, comptime key: []const u8, value: void) !void {
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const bitset = hash(key);
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// most siginificant t bits from hash
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var hash_offset: u5 = t;
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const root_idx = amtIdx(u32, bitset, hash_offset);
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var current: *Node = self.root[root_idx] orelse {
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// node in root table is empty, place the KV here
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const node = try self.allocator.create(Node);
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node.* = .{ .kv = .{ .key = key, .value = value } };
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self.root[root_idx] = node;
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return;
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};
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while (true) {
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const mask = @as(u32, 1) << amtIdx(u32, bitset, hash_offset);
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switch (current.*) {
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.table => |*table| {
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if (table.map & mask == 0) {
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// Empty
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const old_len = @popCount(table.map);
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const new_base = try self.allocator.alloc(Node, old_len + 1);
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var i: u5 = 0;
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for (0..@typeInfo(u32).Int.bits) |shift| {
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const mask_loop = @as(u32, 1) << @intCast(u5, shift);
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if (table.map & mask_loop != 0) {
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defer i += 1;
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const idx = @popCount(table.map & (mask_loop - 1));
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const copy = if (mask == mask_loop) Node{ .kv = Pair{ .key = key, .value = value } } else table.base[idx];
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new_base[i] = copy;
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}
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}
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self.allocator.free(table.base[0..old_len]);
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table.base = new_base.ptr;
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table.map |= mask;
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return; // inserted an elemnt into the Trie
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} else {
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// Found an entry in the array, continue loop (?)
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const idx = @popCount(table.map & (mask - 1));
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current = &table.base[idx];
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hash_offset += t; // Go one layer deper
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}
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},
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.kv => |prev_pair| {
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const prev_bitset = hash(prev_pair.key);
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const prev_mask = @as(u32, 1) << amtIdx(u32, prev_bitset, hash_offset);
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const table = switch (std.math.order(mask, prev_mask)) {
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.lt => blk: {
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// there are no collisions between the two hash subsets.
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const pairs = try self.allocator.alloc(Node, 2);
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pairs[0] = .{ .kv = .{ .key = key, .value = value } };
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pairs[1] = .{ .kv = prev_pair };
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break :blk .{ .table = .{ .map = mask | prev_mask, .base = pairs.ptr } };
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},
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.gt => blk: {
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// there are no collisions between the two hash subsets.
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const pairs = try self.allocator.alloc(Node, 2);
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pairs[0] = .{ .kv = prev_pair };
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pairs[1] = .{ .kv = .{ .key = key, .value = value } };
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break :blk .{ .table = .{ .map = mask | prev_mask, .base = pairs.ptr } };
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},
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.eq => blk: {
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const copied_pair = try self.allocator.alloc(Node, 1);
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copied_pair[0] = .{ .kv = prev_pair };
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break :blk .{ .table = .{ .map = mask, .base = copied_pair.ptr } };
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},
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};
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current.* = table;
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},
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}
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}
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}
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fn walk(node: *const Node, indent: u8) void {
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switch (node.*) {
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.kv => |pair| std.debug.print("{}: {any}\n", .{ indent, pair }),
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.table => |table| {
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const len = @popCount(table.map);
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for (0..len) |i| {
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walk(&table.base[i], indent + 1);
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}
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},
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}
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}
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fn hash(key: []const u8) u32 {
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var result: u32 = 0;
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for (key) |c| result |= @as(u32, 1) << @intCast(u5, c - 'a');
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return result;
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}
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test "insert doesn't panic" {
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var trie = try HashArrayMappedTrie.init(std.testing.allocator);
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defer trie.deinit();
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try trie.insert("hello", {});
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}
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test "search doesn't panic" {
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var trie = try HashArrayMappedTrie.init(std.testing.allocator);
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defer trie.deinit();
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std.debug.assert(trie.search("hello") == null);
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}
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test "insert then search" {
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var trie = try HashArrayMappedTrie.init(std.heap.page_allocator);
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defer trie.deinit();
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// Basic Usage
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try trie.insert("hello", {});
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const test1 = trie.search("hello").?;
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try std.testing.expectEqual(Pair{ .key = "hello", .value = {} }, test1);
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// Collision in Root Node
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try trie.insert("helloworld", {});
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const test2 = trie.search("helloworld").?;
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try std.testing.expectEqual(Pair{ .key = "helloworld", .value = {} }, test2);
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}
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const std = @import("std");
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const HashArrayMappedTrie = @import("HashArrayMappedTrie.zig");
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pub fn main() !void {
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var trie = try HashArrayMappedTrie.init(std.heap.page_allocator);
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defer trie.deinit();
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try trie.insert("hello", {});
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try trie.insert("helloworld", {});
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}
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comptime {
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_ = @import("HashArrayMappedTrie.zig");
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_ = @import("main.zig");
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}
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test {
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@import("std").testing.refAllDecls(@This());
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}
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