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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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38
lib/std/array_list.zig
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@@ -181,7 +181,7 @@ pub fn ArrayListAligned(comptime T: type, comptime alignment: ?u29) type {
// a new buffer and doing our own copy. With a realloc() call,
// the allocator implementation would pointlessly copy our
// extra capacity.
const new_capacity = growCapacity(self.capacity, new_len);
const new_capacity = ArrayListAlignedUnmanaged(T, alignment).growCapacity(self.capacity, new_len);
const old_memory = self.allocatedSlice();
if (self.allocator.remap(old_memory, new_capacity)) |new_memory| {
self.items.ptr = new_memory.ptr;
@@ -446,7 +446,7 @@ pub fn ArrayListAligned(comptime T: type, comptime alignment: ?u29) type {
if (self.capacity >= new_capacity) return;
const better_capacity = growCapacity(self.capacity, new_capacity);
const better_capacity = ArrayListAlignedUnmanaged(T, alignment).growCapacity(self.capacity, new_capacity);
return self.ensureTotalCapacityPrecise(better_capacity);
}
@@ -1062,14 +1062,12 @@ pub fn ArrayListAlignedUnmanaged(comptime T: type, comptime alignment: ?u29) typ
self.capacity = 0;
}
/// If the current capacity is less than `new_capacity`, this function will
/// modify the array so that it can hold at least `new_capacity` items.
/// 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 element pointers if additional memory is needed.
pub fn ensureTotalCapacity(self: *Self, allocator: Allocator, new_capacity: usize) Allocator.Error!void {
pub fn ensureTotalCapacity(self: *Self, gpa: Allocator, new_capacity: usize) Allocator.Error!void {
if (self.capacity >= new_capacity) return;
const better_capacity = growCapacity(self.capacity, new_capacity);
return self.ensureTotalCapacityPrecise(allocator, better_capacity);
return self.ensureTotalCapacityPrecise(gpa, growCapacity(self.capacity, new_capacity));
}
/// If the current capacity is less than `new_capacity`, this function will
@@ -1218,18 +1216,20 @@ pub fn ArrayListAlignedUnmanaged(comptime T: type, comptime alignment: ?u29) typ
if (self.items.len == 0) return null;
return self.getLast();
}
};
}
/// 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) {
new +|= new / 2 + 8;
if (new >= minimum)
return new;
}
const init_capacity = @as(comptime_int, @max(1, std.atomic.cache_line / @sizeOf(T)));
/// 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) {
new +|= new / 2 + init_capacity;
if (new >= minimum)
return new;
}
}
};
}
/// Integer addition returning `error.OutOfMemory` on overflow.