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std.ArrayList: initial capacity based on cache line size

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also std.MultiArrayList
This commit is contained in:
Andrew Kelley
2025-02-11 18:53:13 -08:00
parent 5b9b5e45cb
commit d12123a88c
5 changed files with 47 additions and 32 deletions
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28
lib/std/multi_array_list.zig
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@@ -405,17 +405,27 @@ pub fn MultiArrayList(comptime T: type) type {
/// Modify the array so that it can hold at least `new_capacity` items.
/// Implements super-linear growth to achieve amortized O(1) append operations.
/// Invalidates pointers if additional memory is needed.
pub fn ensureTotalCapacity(self: *Self, gpa: Allocator, new_capacity: usize) !void {
var better_capacity = self.capacity;
if (better_capacity >= new_capacity) return;
/// Invalidates element pointers if additional memory is needed.
pub fn ensureTotalCapacity(self: *Self, gpa: Allocator, new_capacity: usize) Allocator.Error!void {
if (self.capacity >= new_capacity) return;
return self.setCapacity(gpa, growCapacity(self.capacity, new_capacity));
}
const init_capacity = init: {
var max = 1;
for (fields) |field| max = @as(comptime_int, @max(max, @sizeOf(field.type)));
break :init @as(comptime_int, @max(1, std.atomic.cache_line / max));
};
/// Called when memory growth is necessary. Returns a capacity larger than
/// minimum that grows super-linearly.
fn growCapacity(current: usize, minimum: usize) usize {
var new = current;
while (true) {
better_capacity += better_capacity / 2 + 8;
if (better_capacity >= new_capacity) break;
new +|= new / 2 + init_capacity;
if (new >= minimum)
return new;
}
return self.setCapacity(gpa, better_capacity);
}
/// Modify the array so that it can hold at least `additional_count` **more** items.
@@ -838,7 +848,7 @@ test "union" {
try testing.expectEqual(@as(usize, 0), list.items(.tags).len);
try list.ensureTotalCapacity(ally, 2);
try list.ensureTotalCapacity(ally, 3);
list.appendAssumeCapacity(.{ .a = 1 });
list.appendAssumeCapacity(.{ .b = "zigzag" });