fe93332ba2
* implement vector comparison * implement reduce for bool vectors * fix `@memcpy` bug * enable passing std tests
532 lines
20 KiB
Zig
532 lines
20 KiB
Zig
const std = @import("std.zig");
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const assert = std.debug.assert;
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const testing = std.testing;
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const mem = std.mem;
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const Allocator = std.mem.Allocator;
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// Imagine that `fn at(self: *Self, index: usize) &T` is a customer asking for a box
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// from a warehouse, based on a flat array, boxes ordered from 0 to N - 1.
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// But the warehouse actually stores boxes in shelves of increasing powers of 2 sizes.
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// So when the customer requests a box index, we have to translate it to shelf index
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// and box index within that shelf. Illustration:
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//
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// customer indexes:
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// shelf 0: 0
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// shelf 1: 1 2
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// shelf 2: 3 4 5 6
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// shelf 3: 7 8 9 10 11 12 13 14
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// shelf 4: 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
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// 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
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// ...
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//
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// warehouse indexes:
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// shelf 0: 0
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// shelf 1: 0 1
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// shelf 2: 0 1 2 3
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// shelf 3: 0 1 2 3 4 5 6 7
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// shelf 4: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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// 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
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// ...
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//
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// With this arrangement, here are the equations to get the shelf index and
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// box index based on customer box index:
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//
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// shelf_index = floor(log2(customer_index + 1))
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// shelf_count = ceil(log2(box_count + 1))
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// box_index = customer_index + 1 - 2 ** shelf
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// shelf_size = 2 ** shelf_index
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//
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// Now we complicate it a little bit further by adding a preallocated shelf, which must be
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// a power of 2:
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// prealloc=4
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//
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// customer indexes:
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// prealloc: 0 1 2 3
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// shelf 0: 4 5 6 7 8 9 10 11
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// shelf 1: 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
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// 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
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// ...
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//
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// warehouse indexes:
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// prealloc: 0 1 2 3
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// shelf 0: 0 1 2 3 4 5 6 7
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// shelf 1: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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// 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
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// ...
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//
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// Now the equations are:
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//
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// shelf_index = floor(log2(customer_index + prealloc)) - log2(prealloc) - 1
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// shelf_count = ceil(log2(box_count + prealloc)) - log2(prealloc) - 1
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// box_index = customer_index + prealloc - 2 ** (log2(prealloc) + 1 + shelf)
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// shelf_size = prealloc * 2 ** (shelf_index + 1)
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/// This is a stack data structure where pointers to indexes have the same lifetime as the data structure
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/// itself, unlike ArrayList where append() invalidates all existing element pointers.
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/// The tradeoff is that elements are not guaranteed to be contiguous. For that, use ArrayList.
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/// Note however that most elements are contiguous, making this data structure cache-friendly.
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///
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/// Because it never has to copy elements from an old location to a new location, it does not require
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/// its elements to be copyable, and it avoids wasting memory when backed by an ArenaAllocator.
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/// Note that the append() and pop() convenience methods perform a copy, but you can instead use
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/// addOne(), at(), setCapacity(), and shrinkCapacity() to avoid copying items.
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///
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/// This data structure has O(1) append and O(1) pop.
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///
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/// It supports preallocated elements, making it especially well suited when the expected maximum
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/// size is small. `prealloc_item_count` must be 0, or a power of 2.
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pub fn SegmentedList(comptime T: type, comptime prealloc_item_count: usize) type {
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return struct {
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const Self = @This();
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const ShelfIndex = std.math.Log2Int(usize);
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const prealloc_exp: ShelfIndex = blk: {
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// we don't use the prealloc_exp constant when prealloc_item_count is 0
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// but lazy-init may still be triggered by other code so supply a value
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if (prealloc_item_count == 0) {
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break :blk 0;
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} else {
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assert(std.math.isPowerOfTwo(prealloc_item_count));
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const value = std.math.log2_int(usize, prealloc_item_count);
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break :blk value;
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}
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};
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prealloc_segment: [prealloc_item_count]T = undefined,
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dynamic_segments: [][*]T = &[_][*]T{},
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len: usize = 0,
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pub const prealloc_count = prealloc_item_count;
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fn AtType(comptime SelfType: type) type {
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if (@typeInfo(SelfType).Pointer.is_const) {
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return *const T;
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} else {
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return *T;
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}
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}
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pub fn deinit(self: *Self, allocator: Allocator) void {
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self.freeShelves(allocator, @as(ShelfIndex, @intCast(self.dynamic_segments.len)), 0);
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allocator.free(self.dynamic_segments);
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self.* = undefined;
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}
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pub fn at(self: anytype, i: usize) AtType(@TypeOf(self)) {
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assert(i < self.len);
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return self.uncheckedAt(i);
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}
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pub fn count(self: Self) usize {
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return self.len;
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}
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pub fn append(self: *Self, allocator: Allocator, item: T) Allocator.Error!void {
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const new_item_ptr = try self.addOne(allocator);
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new_item_ptr.* = item;
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}
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pub fn appendSlice(self: *Self, allocator: Allocator, items: []const T) Allocator.Error!void {
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for (items) |item| {
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try self.append(allocator, item);
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}
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}
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pub fn pop(self: *Self) ?T {
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if (self.len == 0) return null;
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const index = self.len - 1;
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const result = uncheckedAt(self, index).*;
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self.len = index;
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return result;
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}
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pub fn addOne(self: *Self, allocator: Allocator) Allocator.Error!*T {
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const new_length = self.len + 1;
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try self.growCapacity(allocator, new_length);
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const result = uncheckedAt(self, self.len);
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self.len = new_length;
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return result;
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}
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/// Reduce length to `new_len`.
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/// Invalidates pointers for the elements at index new_len and beyond.
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pub fn shrinkRetainingCapacity(self: *Self, new_len: usize) void {
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assert(new_len <= self.len);
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self.len = new_len;
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}
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/// Invalidates all element pointers.
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pub fn clearRetainingCapacity(self: *Self) void {
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self.len = 0;
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}
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/// Invalidates all element pointers.
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pub fn clearAndFree(self: *Self, allocator: Allocator) void {
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self.setCapacity(allocator, 0) catch unreachable;
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self.len = 0;
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}
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/// Grows or shrinks capacity to match usage.
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/// TODO update this and related methods to match the conventions set by ArrayList
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pub fn setCapacity(self: *Self, allocator: Allocator, new_capacity: usize) Allocator.Error!void {
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if (prealloc_item_count != 0) {
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if (new_capacity <= @as(usize, 1) << (prealloc_exp + @as(ShelfIndex, @intCast(self.dynamic_segments.len)))) {
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return self.shrinkCapacity(allocator, new_capacity);
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}
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}
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return self.growCapacity(allocator, new_capacity);
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}
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/// Only grows capacity, or retains current capacity.
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pub fn growCapacity(self: *Self, allocator: Allocator, new_capacity: usize) Allocator.Error!void {
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const new_cap_shelf_count = shelfCount(new_capacity);
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const old_shelf_count = @as(ShelfIndex, @intCast(self.dynamic_segments.len));
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if (new_cap_shelf_count <= old_shelf_count) return;
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const new_dynamic_segments = try allocator.alloc([*]T, new_cap_shelf_count);
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errdefer allocator.free(new_dynamic_segments);
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var i: ShelfIndex = 0;
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while (i < old_shelf_count) : (i += 1) {
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new_dynamic_segments[i] = self.dynamic_segments[i];
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}
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errdefer while (i > old_shelf_count) : (i -= 1) {
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allocator.free(new_dynamic_segments[i][0..shelfSize(i)]);
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};
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while (i < new_cap_shelf_count) : (i += 1) {
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new_dynamic_segments[i] = (try allocator.alloc(T, shelfSize(i))).ptr;
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}
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allocator.free(self.dynamic_segments);
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self.dynamic_segments = new_dynamic_segments;
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}
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/// Only shrinks capacity or retains current capacity.
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/// It may fail to reduce the capacity in which case the capacity will remain unchanged.
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pub fn shrinkCapacity(self: *Self, allocator: Allocator, new_capacity: usize) void {
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if (new_capacity <= prealloc_item_count) {
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const len = @as(ShelfIndex, @intCast(self.dynamic_segments.len));
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self.freeShelves(allocator, len, 0);
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allocator.free(self.dynamic_segments);
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self.dynamic_segments = &[_][*]T{};
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return;
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}
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const new_cap_shelf_count = shelfCount(new_capacity);
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const old_shelf_count = @as(ShelfIndex, @intCast(self.dynamic_segments.len));
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assert(new_cap_shelf_count <= old_shelf_count);
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if (new_cap_shelf_count == old_shelf_count) return;
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// freeShelves() must be called before resizing the dynamic
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// segments, but we don't know if resizing the dynamic segments
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// will work until we try it. So we must allocate a fresh memory
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// buffer in order to reduce capacity.
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const new_dynamic_segments = allocator.alloc([*]T, new_cap_shelf_count) catch return;
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self.freeShelves(allocator, old_shelf_count, new_cap_shelf_count);
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if (allocator.resize(self.dynamic_segments, new_cap_shelf_count)) {
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// We didn't need the new memory allocation after all.
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self.dynamic_segments = self.dynamic_segments[0..new_cap_shelf_count];
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allocator.free(new_dynamic_segments);
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} else {
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// Good thing we allocated that new memory slice.
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@memcpy(new_dynamic_segments, self.dynamic_segments[0..new_cap_shelf_count]);
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allocator.free(self.dynamic_segments);
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self.dynamic_segments = new_dynamic_segments;
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}
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}
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pub fn shrink(self: *Self, new_len: usize) void {
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assert(new_len <= self.len);
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// TODO take advantage of the new realloc semantics
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self.len = new_len;
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}
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pub fn writeToSlice(self: *Self, dest: []T, start: usize) void {
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const end = start + dest.len;
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assert(end <= self.len);
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var i = start;
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if (end <= prealloc_item_count) {
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const src = self.prealloc_segment[i..end];
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@memcpy(dest[i - start ..][0..src.len], src);
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return;
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} else if (i < prealloc_item_count) {
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const src = self.prealloc_segment[i..];
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@memcpy(dest[i - start ..][0..src.len], src);
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i = prealloc_item_count;
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}
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while (i < end) {
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const shelf_index = shelfIndex(i);
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const copy_start = boxIndex(i, shelf_index);
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const copy_end = @min(shelfSize(shelf_index), copy_start + end - i);
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const src = self.dynamic_segments[shelf_index][copy_start..copy_end];
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@memcpy(dest[i - start ..][0..src.len], src);
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i += (copy_end - copy_start);
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}
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}
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pub fn uncheckedAt(self: anytype, index: usize) AtType(@TypeOf(self)) {
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if (index < prealloc_item_count) {
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return &self.prealloc_segment[index];
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}
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const shelf_index = shelfIndex(index);
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const box_index = boxIndex(index, shelf_index);
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return &self.dynamic_segments[shelf_index][box_index];
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}
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fn shelfCount(box_count: usize) ShelfIndex {
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if (prealloc_item_count == 0) {
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return log2_int_ceil(usize, box_count + 1);
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}
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return log2_int_ceil(usize, box_count + prealloc_item_count) - prealloc_exp - 1;
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}
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fn shelfSize(shelf_index: ShelfIndex) usize {
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if (prealloc_item_count == 0) {
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return @as(usize, 1) << shelf_index;
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}
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return @as(usize, 1) << (shelf_index + (prealloc_exp + 1));
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}
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fn shelfIndex(list_index: usize) ShelfIndex {
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if (prealloc_item_count == 0) {
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return std.math.log2_int(usize, list_index + 1);
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}
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return std.math.log2_int(usize, list_index + prealloc_item_count) - prealloc_exp - 1;
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}
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fn boxIndex(list_index: usize, shelf_index: ShelfIndex) usize {
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if (prealloc_item_count == 0) {
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return (list_index + 1) - (@as(usize, 1) << shelf_index);
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}
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return list_index + prealloc_item_count - (@as(usize, 1) << ((prealloc_exp + 1) + shelf_index));
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}
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fn freeShelves(self: *Self, allocator: Allocator, from_count: ShelfIndex, to_count: ShelfIndex) void {
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var i = from_count;
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while (i != to_count) {
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i -= 1;
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allocator.free(self.dynamic_segments[i][0..shelfSize(i)]);
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}
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}
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pub const Iterator = BaseIterator(*Self, *T);
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pub const ConstIterator = BaseIterator(*const Self, *const T);
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fn BaseIterator(comptime SelfType: type, comptime ElementPtr: type) type {
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return struct {
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list: SelfType,
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index: usize,
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box_index: usize,
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shelf_index: ShelfIndex,
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shelf_size: usize,
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pub fn next(it: *@This()) ?ElementPtr {
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if (it.index >= it.list.len) return null;
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if (it.index < prealloc_item_count) {
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const ptr = &it.list.prealloc_segment[it.index];
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it.index += 1;
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if (it.index == prealloc_item_count) {
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it.box_index = 0;
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it.shelf_index = 0;
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it.shelf_size = prealloc_item_count * 2;
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}
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return ptr;
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}
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const ptr = &it.list.dynamic_segments[it.shelf_index][it.box_index];
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it.index += 1;
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it.box_index += 1;
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if (it.box_index == it.shelf_size) {
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it.shelf_index += 1;
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it.box_index = 0;
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it.shelf_size *= 2;
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}
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return ptr;
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}
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pub fn prev(it: *@This()) ?ElementPtr {
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if (it.index == 0) return null;
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it.index -= 1;
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if (it.index < prealloc_item_count) return &it.list.prealloc_segment[it.index];
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if (it.box_index == 0) {
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it.shelf_index -= 1;
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it.shelf_size /= 2;
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it.box_index = it.shelf_size - 1;
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} else {
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it.box_index -= 1;
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}
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return &it.list.dynamic_segments[it.shelf_index][it.box_index];
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}
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pub fn peek(it: *@This()) ?ElementPtr {
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if (it.index >= it.list.len)
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return null;
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if (it.index < prealloc_item_count)
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return &it.list.prealloc_segment[it.index];
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return &it.list.dynamic_segments[it.shelf_index][it.box_index];
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}
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pub fn set(it: *@This(), index: usize) void {
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it.index = index;
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if (index < prealloc_item_count) return;
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it.shelf_index = shelfIndex(index);
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it.box_index = boxIndex(index, it.shelf_index);
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it.shelf_size = shelfSize(it.shelf_index);
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}
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};
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}
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pub fn iterator(self: *Self, start_index: usize) Iterator {
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var it = Iterator{
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.list = self,
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.index = undefined,
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.shelf_index = undefined,
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.box_index = undefined,
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.shelf_size = undefined,
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};
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it.set(start_index);
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return it;
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}
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pub fn constIterator(self: *const Self, start_index: usize) ConstIterator {
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var it = ConstIterator{
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.list = self,
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.index = undefined,
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.shelf_index = undefined,
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.box_index = undefined,
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.shelf_size = undefined,
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};
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it.set(start_index);
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return it;
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}
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};
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}
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test "SegmentedList basic usage" {
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try testSegmentedList(0);
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try testSegmentedList(1);
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try testSegmentedList(2);
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try testSegmentedList(4);
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try testSegmentedList(8);
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try testSegmentedList(16);
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}
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fn testSegmentedList(comptime prealloc: usize) !void {
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var list = SegmentedList(i32, prealloc){};
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defer list.deinit(testing.allocator);
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{
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var i: usize = 0;
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while (i < 100) : (i += 1) {
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try list.append(testing.allocator, @as(i32, @intCast(i + 1)));
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try testing.expect(list.len == i + 1);
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}
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}
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{
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var i: usize = 0;
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while (i < 100) : (i += 1) {
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try testing.expect(list.at(i).* == @as(i32, @intCast(i + 1)));
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}
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}
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{
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var it = list.iterator(0);
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var x: i32 = 0;
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while (it.next()) |item| {
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x += 1;
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try testing.expect(item.* == x);
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}
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try testing.expect(x == 100);
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while (it.prev()) |item| : (x -= 1) {
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try testing.expect(item.* == x);
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}
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try testing.expect(x == 0);
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}
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{
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var it = list.constIterator(0);
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var x: i32 = 0;
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while (it.next()) |item| {
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x += 1;
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try testing.expect(item.* == x);
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}
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try testing.expect(x == 100);
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while (it.prev()) |item| : (x -= 1) {
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try testing.expect(item.* == x);
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}
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try testing.expect(x == 0);
|
|
}
|
|
|
|
try testing.expect(list.pop().? == 100);
|
|
try testing.expect(list.len == 99);
|
|
|
|
try list.appendSlice(testing.allocator, &[_]i32{ 1, 2, 3 });
|
|
try testing.expect(list.len == 102);
|
|
try testing.expect(list.pop().? == 3);
|
|
try testing.expect(list.pop().? == 2);
|
|
try testing.expect(list.pop().? == 1);
|
|
try testing.expect(list.len == 99);
|
|
|
|
try list.appendSlice(testing.allocator, &[_]i32{});
|
|
try testing.expect(list.len == 99);
|
|
|
|
{
|
|
var i: i32 = 99;
|
|
while (list.pop()) |item| : (i -= 1) {
|
|
try testing.expect(item == i);
|
|
list.shrinkCapacity(testing.allocator, list.len);
|
|
}
|
|
}
|
|
|
|
{
|
|
var control: [100]i32 = undefined;
|
|
var dest: [100]i32 = undefined;
|
|
|
|
var i: i32 = 0;
|
|
while (i < 100) : (i += 1) {
|
|
try list.append(testing.allocator, i + 1);
|
|
control[@as(usize, @intCast(i))] = i + 1;
|
|
}
|
|
|
|
@memset(dest[0..], 0);
|
|
list.writeToSlice(dest[0..], 0);
|
|
try testing.expect(mem.eql(i32, control[0..], dest[0..]));
|
|
|
|
@memset(dest[0..], 0);
|
|
list.writeToSlice(dest[50..], 50);
|
|
try testing.expect(mem.eql(i32, control[50..], dest[50..]));
|
|
}
|
|
|
|
try list.setCapacity(testing.allocator, 0);
|
|
}
|
|
|
|
test "std.segmented_list clearRetainingCapacity" {
|
|
var list = SegmentedList(i32, 1){};
|
|
defer list.deinit(testing.allocator);
|
|
|
|
try list.appendSlice(testing.allocator, &[_]i32{ 4, 5 });
|
|
list.clearRetainingCapacity();
|
|
try list.append(testing.allocator, 6);
|
|
try testing.expect(list.at(0).* == 6);
|
|
try testing.expect(list.len == 1);
|
|
list.clearRetainingCapacity();
|
|
try testing.expect(list.len == 0);
|
|
}
|
|
|
|
/// TODO look into why this std.math function was changed in
|
|
/// fc9430f56798a53f9393a697f4ccd6bf9981b970.
|
|
fn log2_int_ceil(comptime T: type, x: T) std.math.Log2Int(T) {
|
|
assert(x != 0);
|
|
const log2_val = std.math.log2_int(T, x);
|
|
if (@as(T, 1) << log2_val == x)
|
|
return log2_val;
|
|
return log2_val + 1;
|
|
}
|