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| 1 | | // SPDX-License-Identifier: MIT |
| 2 | | // Copyright (c) 2015-2020 Zig Contributors |
| 3 | | // This file is part of [zig](https://ziglang.org/), which is MIT licensed. |
| 4 | | // The MIT license requires this copyright notice to be included in all copies |
| 5 | | // and substantial portions of the software. |
| 6 | | const std = @import("std.zig"); |
| 7 | | const assert = std.debug.assert; |
| 8 | | const testing = std.testing; |
| 9 | | const Allocator = std.mem.Allocator; |
| 10 | | |
| 11 | | // Imagine that `fn at(self: *Self, index: usize) &T` is a customer asking for a box |
| 12 | | // from a warehouse, based on a flat array, boxes ordered from 0 to N - 1. |
| 13 | | // But the warehouse actually stores boxes in shelves of increasing powers of 2 sizes. |
| 14 | | // So when the customer requests a box index, we have to translate it to shelf index |
| 15 | | // and box index within that shelf. Illustration: |
| 16 | | // |
| 17 | | // customer indexes: |
| 18 | | // shelf 0: 0 |
| 19 | | // shelf 1: 1 2 |
| 20 | | // shelf 2: 3 4 5 6 |
| 21 | | // shelf 3: 7 8 9 10 11 12 13 14 |
| 22 | | // shelf 4: 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 |
| 23 | | // shelf 5: 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 |
| 24 | | // ... |
| 25 | | // |
| 26 | | // warehouse indexes: |
| 27 | | // shelf 0: 0 |
| 28 | | // shelf 1: 0 1 |
| 29 | | // shelf 2: 0 1 2 3 |
| 30 | | // shelf 3: 0 1 2 3 4 5 6 7 |
| 31 | | // shelf 4: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
| 32 | | // shelf 5: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 |
| 33 | | // ... |
| 34 | | // |
| 35 | | // With this arrangement, here are the equations to get the shelf index and |
| 36 | | // box index based on customer box index: |
| 37 | | // |
| 38 | | // shelf_index = floor(log2(customer_index + 1)) |
| 39 | | // shelf_count = ceil(log2(box_count + 1)) |
| 40 | | // box_index = customer_index + 1 - 2 ** shelf |
| 41 | | // shelf_size = 2 ** shelf_index |
| 42 | | // |
| 43 | | // Now we complicate it a little bit further by adding a preallocated shelf, which must be |
| 44 | | // a power of 2: |
| 45 | | // prealloc=4 |
| 46 | | // |
| 47 | | // customer indexes: |
| 48 | | // prealloc: 0 1 2 3 |
| 49 | | // shelf 0: 4 5 6 7 8 9 10 11 |
| 50 | | // shelf 1: 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 |
| 51 | | // shelf 2: 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 |
| 52 | | // ... |
| 53 | | // |
| 54 | | // warehouse indexes: |
| 55 | | // prealloc: 0 1 2 3 |
| 56 | | // shelf 0: 0 1 2 3 4 5 6 7 |
| 57 | | // shelf 1: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
| 58 | | // shelf 2: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 |
| 59 | | // ... |
| 60 | | // |
| 61 | | // Now the equations are: |
| 62 | | // |
| 63 | | // shelf_index = floor(log2(customer_index + prealloc)) - log2(prealloc) - 1 |
| 64 | | // shelf_count = ceil(log2(box_count + prealloc)) - log2(prealloc) - 1 |
| 65 | | // box_index = customer_index + prealloc - 2 ** (log2(prealloc) + 1 + shelf) |
| 66 | | // shelf_size = prealloc * 2 ** (shelf_index + 1) |
| 67 | | |
| 68 | | /// This is a stack data structure where pointers to indexes have the same lifetime as the data structure |
| 69 | | /// itself, unlike ArrayList where push() invalidates all existing element pointers. |
| 70 | | /// The tradeoff is that elements are not guaranteed to be contiguous. For that, use ArrayList. |
| 71 | | /// Note however that most elements are contiguous, making this data structure cache-friendly. |
| 72 | | /// |
| 73 | | /// Because it never has to copy elements from an old location to a new location, it does not require |
| 74 | | /// its elements to be copyable, and it avoids wasting memory when backed by an ArenaAllocator. |
| 75 | | /// Note that the push() and pop() convenience methods perform a copy, but you can instead use |
| 76 | | /// addOne(), at(), setCapacity(), and shrinkCapacity() to avoid copying items. |
| 77 | | /// |
| 78 | | /// This data structure has O(1) push and O(1) pop. |
| 79 | | /// |
| 80 | | /// It supports preallocated elements, making it especially well suited when the expected maximum |
| 81 | | /// size is small. `prealloc_item_count` must be 0, or a power of 2. |
| 82 | | pub fn SegmentedList(comptime T: type, comptime prealloc_item_count: usize) type { |
| 83 | | return struct { |
| 84 | | const Self = @This(); |
| 85 | | const ShelfIndex = std.math.Log2Int(usize); |
| 86 | | |
| 87 | | const prealloc_exp: ShelfIndex = blk: { |
| 88 | | // we don't use the prealloc_exp constant when prealloc_item_count is 0 |
| 89 | | // but lazy-init may still be triggered by other code so supply a value |
| 90 | | if (prealloc_item_count == 0) { |
| 91 | | break :blk 0; |
| 92 | | } else { |
| 93 | | assert(std.math.isPowerOfTwo(prealloc_item_count)); |
| 94 | | const value = std.math.log2_int(usize, prealloc_item_count); |
| 95 | | break :blk value; |
| 96 | | } |
| 97 | | }; |
| 98 | | |
| 99 | | prealloc_segment: [prealloc_item_count]T, |
| 100 | | dynamic_segments: [][*]T, |
| 101 | | allocator: *Allocator, |
| 102 | | len: usize, |
| 103 | | |
| 104 | | pub const prealloc_count = prealloc_item_count; |
| 105 | | |
| 106 | | fn AtType(comptime SelfType: type) type { |
| 107 | | if (@typeInfo(SelfType).Pointer.is_const) { |
| 108 | | return *const T; |
| 109 | | } else { |
| 110 | | return *T; |
| 111 | | } |
| 112 | | } |
| 113 | | |
| 114 | | /// Deinitialize with `deinit` |
| 115 | | pub fn init(allocator: *Allocator) Self { |
| 116 | | return Self{ |
| 117 | | .allocator = allocator, |
| 118 | | .len = 0, |
| 119 | | .prealloc_segment = undefined, |
| 120 | | .dynamic_segments = &[_][*]T{}, |
| 121 | | }; |
| 122 | | } |
| 123 | | |
| 124 | | pub fn deinit(self: *Self) void { |
| 125 | | self.freeShelves(@intCast(ShelfIndex, self.dynamic_segments.len), 0); |
| 126 | | self.allocator.free(self.dynamic_segments); |
| 127 | | self.* = undefined; |
| 128 | | } |
| 129 | | |
| 130 | | pub fn at(self: anytype, i: usize) AtType(@TypeOf(self)) { |
| 131 | | assert(i < self.len); |
| 132 | | return self.uncheckedAt(i); |
| 133 | | } |
| 134 | | |
| 135 | | pub fn count(self: Self) usize { |
| 136 | | return self.len; |
| 137 | | } |
| 138 | | |
| 139 | | pub fn push(self: *Self, item: T) !void { |
| 140 | | const new_item_ptr = try self.addOne(); |
| 141 | | new_item_ptr.* = item; |
| 142 | | } |
| 143 | | |
| 144 | | pub fn pushMany(self: *Self, items: []const T) !void { |
| 145 | | for (items) |item| { |
| 146 | | try self.push(item); |
| 147 | | } |
| 148 | | } |
| 149 | | |
| 150 | | pub fn pop(self: *Self) ?T { |
| 151 | | if (self.len == 0) return null; |
| 152 | | |
| 153 | | const index = self.len - 1; |
| 154 | | const result = uncheckedAt(self, index).*; |
| 155 | | self.len = index; |
| 156 | | return result; |
| 157 | | } |
| 158 | | |
| 159 | | pub fn addOne(self: *Self) !*T { |
| 160 | | const new_length = self.len + 1; |
| 161 | | try self.growCapacity(new_length); |
| 162 | | const result = uncheckedAt(self, self.len); |
| 163 | | self.len = new_length; |
| 164 | | return result; |
| 165 | | } |
| 166 | | |
| 167 | | /// Grows or shrinks capacity to match usage. |
| 168 | | pub fn setCapacity(self: *Self, new_capacity: usize) !void { |
| 169 | | if (prealloc_item_count != 0) { |
| 170 | | if (new_capacity <= @as(usize, 1) << (prealloc_exp + @intCast(ShelfIndex, self.dynamic_segments.len))) { |
| 171 | | return self.shrinkCapacity(new_capacity); |
| 172 | | } |
| 173 | | } |
| 174 | | return self.growCapacity(new_capacity); |
| 175 | | } |
| 176 | | |
| 177 | | /// Only grows capacity, or retains current capacity |
| 178 | | pub fn growCapacity(self: *Self, new_capacity: usize) !void { |
| 179 | | const new_cap_shelf_count = shelfCount(new_capacity); |
| 180 | | const old_shelf_count = @intCast(ShelfIndex, self.dynamic_segments.len); |
| 181 | | if (new_cap_shelf_count > old_shelf_count) { |
| 182 | | self.dynamic_segments = try self.allocator.realloc(self.dynamic_segments, new_cap_shelf_count); |
| 183 | | var i = old_shelf_count; |
| 184 | | errdefer { |
| 185 | | self.freeShelves(i, old_shelf_count); |
| 186 | | self.dynamic_segments = self.allocator.shrink(self.dynamic_segments, old_shelf_count); |
| 187 | | } |
| 188 | | while (i < new_cap_shelf_count) : (i += 1) { |
| 189 | | self.dynamic_segments[i] = (try self.allocator.alloc(T, shelfSize(i))).ptr; |
| 190 | | } |
| 191 | | } |
| 192 | | } |
| 193 | | |
| 194 | | /// Only shrinks capacity or retains current capacity |
| 195 | | pub fn shrinkCapacity(self: *Self, new_capacity: usize) void { |
| 196 | | if (new_capacity <= prealloc_item_count) { |
| 197 | | const len = @intCast(ShelfIndex, self.dynamic_segments.len); |
| 198 | | self.freeShelves(len, 0); |
| 199 | | self.allocator.free(self.dynamic_segments); |
| 200 | | self.dynamic_segments = &[_][*]T{}; |
| 201 | | return; |
| 202 | | } |
| 203 | | |
| 204 | | const new_cap_shelf_count = shelfCount(new_capacity); |
| 205 | | const old_shelf_count = @intCast(ShelfIndex, self.dynamic_segments.len); |
| 206 | | assert(new_cap_shelf_count <= old_shelf_count); |
| 207 | | if (new_cap_shelf_count == old_shelf_count) { |
| 208 | | return; |
| 209 | | } |
| 210 | | |
| 211 | | self.freeShelves(old_shelf_count, new_cap_shelf_count); |
| 212 | | self.dynamic_segments = self.allocator.shrink(self.dynamic_segments, new_cap_shelf_count); |
| 213 | | } |
| 214 | | |
| 215 | | pub fn shrink(self: *Self, new_len: usize) void { |
| 216 | | assert(new_len <= self.len); |
| 217 | | // TODO take advantage of the new realloc semantics |
| 218 | | self.len = new_len; |
| 219 | | } |
| 220 | | |
| 221 | | pub fn writeToSlice(self: *Self, dest: []T, start: usize) void { |
| 222 | | const end = start + dest.len; |
| 223 | | assert(end <= self.len); |
| 224 | | |
| 225 | | var i = start; |
| 226 | | if (end <= prealloc_item_count) { |
| 227 | | std.mem.copy(T, dest[i - start ..], self.prealloc_segment[i..end]); |
| 228 | | return; |
| 229 | | } else if (i < prealloc_item_count) { |
| 230 | | std.mem.copy(T, dest[i - start ..], self.prealloc_segment[i..]); |
| 231 | | i = prealloc_item_count; |
| 232 | | } |
| 233 | | |
| 234 | | while (i < end) { |
| 235 | | const shelf_index = shelfIndex(i); |
| 236 | | const copy_start = boxIndex(i, shelf_index); |
| 237 | | const copy_end = std.math.min(shelfSize(shelf_index), copy_start + end - i); |
| 238 | | |
| 239 | | std.mem.copy( |
| 240 | | T, |
| 241 | | dest[i - start ..], |
| 242 | | self.dynamic_segments[shelf_index][copy_start..copy_end], |
| 243 | | ); |
| 244 | | |
| 245 | | i += (copy_end - copy_start); |
| 246 | | } |
| 247 | | } |
| 248 | | |
| 249 | | pub fn uncheckedAt(self: anytype, index: usize) AtType(@TypeOf(self)) { |
| 250 | | if (index < prealloc_item_count) { |
| 251 | | return &self.prealloc_segment[index]; |
| 252 | | } |
| 253 | | const shelf_index = shelfIndex(index); |
| 254 | | const box_index = boxIndex(index, shelf_index); |
| 255 | | return &self.dynamic_segments[shelf_index][box_index]; |
| 256 | | } |
| 257 | | |
| 258 | | fn shelfCount(box_count: usize) ShelfIndex { |
| 259 | | if (prealloc_item_count == 0) { |
| 260 | | return std.math.log2_int_ceil(usize, box_count + 1); |
| 261 | | } |
| 262 | | return std.math.log2_int_ceil(usize, box_count + prealloc_item_count) - prealloc_exp - 1; |
| 263 | | } |
| 264 | | |
| 265 | | fn shelfSize(shelf_index: ShelfIndex) usize { |
| 266 | | if (prealloc_item_count == 0) { |
| 267 | | return @as(usize, 1) << shelf_index; |
| 268 | | } |
| 269 | | return @as(usize, 1) << (shelf_index + (prealloc_exp + 1)); |
| 270 | | } |
| 271 | | |
| 272 | | fn shelfIndex(list_index: usize) ShelfIndex { |
| 273 | | if (prealloc_item_count == 0) { |
| 274 | | return std.math.log2_int(usize, list_index + 1); |
| 275 | | } |
| 276 | | return std.math.log2_int(usize, list_index + prealloc_item_count) - prealloc_exp - 1; |
| 277 | | } |
| 278 | | |
| 279 | | fn boxIndex(list_index: usize, shelf_index: ShelfIndex) usize { |
| 280 | | if (prealloc_item_count == 0) { |
| 281 | | return (list_index + 1) - (@as(usize, 1) << shelf_index); |
| 282 | | } |
| 283 | | return list_index + prealloc_item_count - (@as(usize, 1) << ((prealloc_exp + 1) + shelf_index)); |
| 284 | | } |
| 285 | | |
| 286 | | fn freeShelves(self: *Self, from_count: ShelfIndex, to_count: ShelfIndex) void { |
| 287 | | var i = from_count; |
| 288 | | while (i != to_count) { |
| 289 | | i -= 1; |
| 290 | | self.allocator.free(self.dynamic_segments[i][0..shelfSize(i)]); |
| 291 | | } |
| 292 | | } |
| 293 | | |
| 294 | | pub const Iterator = struct { |
| 295 | | list: *Self, |
| 296 | | index: usize, |
| 297 | | box_index: usize, |
| 298 | | shelf_index: ShelfIndex, |
| 299 | | shelf_size: usize, |
| 300 | | |
| 301 | | pub fn next(it: *Iterator) ?*T { |
| 302 | | if (it.index >= it.list.len) return null; |
| 303 | | if (it.index < prealloc_item_count) { |
| 304 | | const ptr = &it.list.prealloc_segment[it.index]; |
| 305 | | it.index += 1; |
| 306 | | if (it.index == prealloc_item_count) { |
| 307 | | it.box_index = 0; |
| 308 | | it.shelf_index = 0; |
| 309 | | it.shelf_size = prealloc_item_count * 2; |
| 310 | | } |
| 311 | | return ptr; |
| 312 | | } |
| 313 | | |
| 314 | | const ptr = &it.list.dynamic_segments[it.shelf_index][it.box_index]; |
| 315 | | it.index += 1; |
| 316 | | it.box_index += 1; |
| 317 | | if (it.box_index == it.shelf_size) { |
| 318 | | it.shelf_index += 1; |
| 319 | | it.box_index = 0; |
| 320 | | it.shelf_size *= 2; |
| 321 | | } |
| 322 | | return ptr; |
| 323 | | } |
| 324 | | |
| 325 | | pub fn prev(it: *Iterator) ?*T { |
| 326 | | if (it.index == 0) return null; |
| 327 | | |
| 328 | | it.index -= 1; |
| 329 | | if (it.index < prealloc_item_count) return &it.list.prealloc_segment[it.index]; |
| 330 | | |
| 331 | | if (it.box_index == 0) { |
| 332 | | it.shelf_index -= 1; |
| 333 | | it.shelf_size /= 2; |
| 334 | | it.box_index = it.shelf_size - 1; |
| 335 | | } else { |
| 336 | | it.box_index -= 1; |
| 337 | | } |
| 338 | | |
| 339 | | return &it.list.dynamic_segments[it.shelf_index][it.box_index]; |
| 340 | | } |
| 341 | | |
| 342 | | pub fn peek(it: *Iterator) ?*T { |
| 343 | | if (it.index >= it.list.len) |
| 344 | | return null; |
| 345 | | if (it.index < prealloc_item_count) |
| 346 | | return &it.list.prealloc_segment[it.index]; |
| 347 | | |
| 348 | | return &it.list.dynamic_segments[it.shelf_index][it.box_index]; |
| 349 | | } |
| 350 | | |
| 351 | | pub fn set(it: *Iterator, index: usize) void { |
| 352 | | it.index = index; |
| 353 | | if (index < prealloc_item_count) return; |
| 354 | | it.shelf_index = shelfIndex(index); |
| 355 | | it.box_index = boxIndex(index, it.shelf_index); |
| 356 | | it.shelf_size = shelfSize(it.shelf_index); |
| 357 | | } |
| 358 | | }; |
| 359 | | |
| 360 | | pub fn iterator(self: *Self, start_index: usize) Iterator { |
| 361 | | var it = Iterator{ |
| 362 | | .list = self, |
| 363 | | .index = undefined, |
| 364 | | .shelf_index = undefined, |
| 365 | | .box_index = undefined, |
| 366 | | .shelf_size = undefined, |
| 367 | | }; |
| 368 | | it.set(start_index); |
| 369 | | return it; |
| 370 | | } |
| 371 | | }; |
| 372 | | } |
| 373 | | |
| 374 | | test "std.SegmentedList" { |
| 375 | | var a = std.testing.allocator; |
| 376 | | |
| 377 | | try testSegmentedList(0, a); |
| 378 | | try testSegmentedList(1, a); |
| 379 | | try testSegmentedList(2, a); |
| 380 | | try testSegmentedList(4, a); |
| 381 | | try testSegmentedList(8, a); |
| 382 | | try testSegmentedList(16, a); |
| 383 | | } |
| 384 | | |
| 385 | | fn testSegmentedList(comptime prealloc: usize, allocator: *Allocator) !void { |
| 386 | | var list = SegmentedList(i32, prealloc).init(allocator); |
| 387 | | defer list.deinit(); |
| 388 | | |
| 389 | | { |
| 390 | | var i: usize = 0; |
| 391 | | while (i < 100) : (i += 1) { |
| 392 | | try list.push(@intCast(i32, i + 1)); |
| 393 | | testing.expect(list.len == i + 1); |
| 394 | | } |
| 395 | | } |
| 396 | | |
| 397 | | { |
| 398 | | var i: usize = 0; |
| 399 | | while (i < 100) : (i += 1) { |
| 400 | | testing.expect(list.at(i).* == @intCast(i32, i + 1)); |
| 401 | | } |
| 402 | | } |
| 403 | | |
| 404 | | { |
| 405 | | var it = list.iterator(0); |
| 406 | | var x: i32 = 0; |
| 407 | | while (it.next()) |item| { |
| 408 | | x += 1; |
| 409 | | testing.expect(item.* == x); |
| 410 | | } |
| 411 | | testing.expect(x == 100); |
| 412 | | while (it.prev()) |item| : (x -= 1) { |
| 413 | | testing.expect(item.* == x); |
| 414 | | } |
| 415 | | testing.expect(x == 0); |
| 416 | | } |
| 417 | | |
| 418 | | testing.expect(list.pop().? == 100); |
| 419 | | testing.expect(list.len == 99); |
| 420 | | |
| 421 | | try list.pushMany(&[_]i32{ 1, 2, 3 }); |
| 422 | | testing.expect(list.len == 102); |
| 423 | | testing.expect(list.pop().? == 3); |
| 424 | | testing.expect(list.pop().? == 2); |
| 425 | | testing.expect(list.pop().? == 1); |
| 426 | | testing.expect(list.len == 99); |
| 427 | | |
| 428 | | try list.pushMany(&[_]i32{}); |
| 429 | | testing.expect(list.len == 99); |
| 430 | | |
| 431 | | { |
| 432 | | var i: i32 = 99; |
| 433 | | while (list.pop()) |item| : (i -= 1) { |
| 434 | | testing.expect(item == i); |
| 435 | | list.shrinkCapacity(list.len); |
| 436 | | } |
| 437 | | } |
| 438 | | |
| 439 | | { |
| 440 | | var control: [100]i32 = undefined; |
| 441 | | var dest: [100]i32 = undefined; |
| 442 | | |
| 443 | | var i: i32 = 0; |
| 444 | | while (i < 100) : (i += 1) { |
| 445 | | try list.push(i + 1); |
| 446 | | control[@intCast(usize, i)] = i + 1; |
| 447 | | } |
| 448 | | |
| 449 | | std.mem.set(i32, dest[0..], 0); |
| 450 | | list.writeToSlice(dest[0..], 0); |
| 451 | | testing.expect(std.mem.eql(i32, control[0..], dest[0..])); |
| 452 | | |
| 453 | | std.mem.set(i32, dest[0..], 0); |
| 454 | | list.writeToSlice(dest[50..], 50); |
| 455 | | testing.expect(std.mem.eql(i32, control[50..], dest[50..])); |
| 456 | | } |
| 457 | | |
| 458 | | try list.setCapacity(0); |
| 459 | | } |
Andrew Kelley <andrew@ziglang.org> 2020-11-30 13:03:10-07:00