authorgravatar for andrew@ziglang.orgAndrew Kelley <andrew@ziglang.org> 2024-08-23 22:30:10-07:00
committergravatar for andrew@ziglang.orgAndrew Kelley <andrew@ziglang.org> 2024-08-23 22:30:10-07:00
log85747b266aac8a2ff7fea4a4b18f722133544ad7
tree53759fbc1840205ba142d257cc8640a62357750e
parentd9e8671d963dc99ec8b4721f53d77828efa232ed

Revert "Smaller memory footprint for BoundedArray (#16299)"

This reverts commit cb5a6be41ae0efc30d0b59a41b0763db966e5bf4. I deeply apologize for the churn. This change is problematic given that we do not have ranged integers (yet? see #3806). In the meantime, this type needs to be `usize`, matching the length and index types for all std lib data structures. Users who want to save memory should not use heap-allocated BoundedArray values, since it is inherently memory-inefficient. Use a different memory layout instead. If #3806 is accepted and implemented, the length value can become an integer with the appropriate range, without the footgun. If that proposal is not accepted, len type will remain a usize.

1 files changed, 8 insertions(+), 22 deletions(-)

lib/std/bounded_array.zig+8-22
......@@ -39,16 +39,14 @@ pub fn BoundedArrayAligned(
3939) type {
4040 return struct {
4141 const Self = @This();
42 const Len = std.math.IntFittingRange(0, buffer_capacity);
43
4442 buffer: [buffer_capacity]T align(alignment) = undefined,
45 len: Len = 0,
43 len: usize = 0,
4644
4745 /// Set the actual length of the slice.
4846 /// Returns error.Overflow if it exceeds the length of the backing array.
4947 pub fn init(len: usize) error{Overflow}!Self {
5048 if (len > buffer_capacity) return error.Overflow;
51 return Self{ .len = @intCast(len) };
49 return Self{ .len = len };
5250 }
5351
5452 /// View the internal array as a slice whose size was previously set.
......@@ -69,7 +67,7 @@ pub fn BoundedArrayAligned(
6967 /// Does not initialize added items if any.
7068 pub fn resize(self: *Self, len: usize) error{Overflow}!void {
7169 if (len > buffer_capacity) return error.Overflow;
72 self.len = @intCast(len);
70 self.len = len;
7371 }
7472
7573 /// Remove all elements from the slice.
......@@ -178,7 +176,7 @@ pub fn BoundedArrayAligned(
178176 /// This operation is O(N).
179177 pub fn insertSlice(self: *Self, i: usize, items: []const T) error{Overflow}!void {
180178 try self.ensureUnusedCapacity(items.len);
181 self.len = @intCast(self.len + items.len);
179 self.len += items.len;
182180 mem.copyBackwards(T, self.slice()[i + items.len .. self.len], self.constSlice()[i .. self.len - items.len]);
183181 @memcpy(self.slice()[i..][0..items.len], items);
184182 }
......@@ -208,7 +206,7 @@ pub fn BoundedArrayAligned(
208206 for (self.constSlice()[after_range..], 0..) |item, i| {
209207 self.slice()[after_subrange..][i] = item;
210208 }
211 self.len = @intCast(self.len - len + new_items.len);
209 self.len -= len - new_items.len;
212210 }
213211 }
214212
......@@ -259,7 +257,7 @@ pub fn BoundedArrayAligned(
259257 /// enough to store the new items.
260258 pub fn appendSliceAssumeCapacity(self: *Self, items: []const T) void {
261259 const old_len = self.len;
262 self.len = @intCast(self.len + items.len);
260 self.len += items.len;
263261 @memcpy(self.slice()[old_len..][0..items.len], items);
264262 }
265263
......@@ -275,8 +273,8 @@ pub fn BoundedArrayAligned(
275273 /// Asserts the capacity is enough.
276274 pub fn appendNTimesAssumeCapacity(self: *Self, value: T, n: usize) void {
277275 const old_len = self.len;
278 assert(self.len + n <= buffer_capacity);
279 self.len = @intCast(self.len + n);
276 self.len += n;
277 assert(self.len <= buffer_capacity);
280278 @memset(self.slice()[old_len..self.len], value);
281279 }
282280
......@@ -406,18 +404,6 @@ test BoundedArray {
406404 try testing.expectEqualStrings(s, a.constSlice());
407405}
408406
409test "BoundedArray sizeOf" {
410 // Just sanity check size on one CPU
411 if (@import("builtin").cpu.arch != .x86_64)
412 return;
413
414 try testing.expectEqual(@sizeOf(BoundedArray(u8, 3)), 4);
415
416 // `len` is the minimum required size to hold the maximum capacity
417 try testing.expectEqual(@TypeOf(@as(BoundedArray(u8, 15), undefined).len), u4);
418 try testing.expectEqual(@TypeOf(@as(BoundedArray(u8, 16), undefined).len), u5);
419}
420
421407test "BoundedArrayAligned" {
422408 var a = try BoundedArrayAligned(u8, 16, 4).init(0);
423409 try a.append(0);