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SegmentedList: fixups from review comments

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This commit is contained in:
Andrew Kelley 2018-05-07 09:53:52 -04:00
parent 41e1cd185b
commit 81007d0a4b
1 changed files with 15 additions and 11 deletions
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26
std/segmented_list.zig
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@ -18,12 +18,12 @@ const Allocator = std.mem.Allocator;
// ...
//
// warehouse indexes:
// shelf 0: 0
// shelf 1: 0 1
// shelf 2: 0 1 2 3
// shelf 3: 0 1 2 3 4 5 6 7
// shelf 4: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
// 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
// shelf 0: 0
// shelf 1: 0 1
// shelf 2: 0 1 2 3
// shelf 3: 0 1 2 3 4 5 6 7
// shelf 4: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
// 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
// ...
//
// With this arrangement, here are the equations to get the shelf index and
@ -66,6 +66,8 @@ const Allocator = std.mem.Allocator;
///
/// Because it never has to copy elements from an old location to a new location, it does not require
/// its elements to be copyable, and it avoids wasting memory when backed by an ArenaAllocator.
/// Note that the push() and pop() convenience methods perform a copy, but you can instead use
/// addOne(), at(), setCapacity(), and shrinkCapacity() to avoid copying items.
///
/// This data structure has O(1) push and O(1) pop.
///
@ -74,8 +76,10 @@ const Allocator = std.mem.Allocator;
pub fn SegmentedList(comptime T: type, comptime prealloc_item_count: usize) type {
return struct {
const Self = this;
const prealloc_base = blk: {
const prealloc_exp = blk: {
// we don't use the prealloc_exp constant when prealloc_item_count is 0.
assert(prealloc_item_count != 0);
const value = std.math.log2_int(usize, prealloc_item_count);
assert((1 << value) == prealloc_item_count); // prealloc_item_count must be a power of 2
break :blk @typeOf(1)(value);
@ -190,28 +194,28 @@ pub fn SegmentedList(comptime T: type, comptime prealloc_item_count: usize) type
if (prealloc_item_count == 0) {
return std.math.log2_int_ceil(usize, box_count + 1);
}
return std.math.log2_int_ceil(usize, box_count + prealloc_item_count) - prealloc_base - 1;
return std.math.log2_int_ceil(usize, box_count + prealloc_item_count) - prealloc_exp - 1;
}
fn shelfSize(shelf_index: ShelfIndex) usize {
if (prealloc_item_count == 0) {
return usize(1) << shelf_index;
}
return usize(1) << (shelf_index + (prealloc_base + 1));
return usize(1) << (shelf_index + (prealloc_exp + 1));
}
fn shelfIndex(list_index: usize) ShelfIndex {
if (prealloc_item_count == 0) {
return std.math.log2_int(usize, list_index + 1);
}
return std.math.log2_int(usize, list_index + prealloc_item_count) - prealloc_base - 1;
return std.math.log2_int(usize, list_index + prealloc_item_count) - prealloc_exp - 1;
}
fn boxIndex(list_index: usize, shelf_index: ShelfIndex) usize {
if (prealloc_item_count == 0) {
return (list_index + 1) - (usize(1) << shelf_index);
}
return list_index + prealloc_item_count - (usize(1) << ((prealloc_base + 1) + shelf_index));
return list_index + prealloc_item_count - (usize(1) << ((prealloc_exp + 1) + shelf_index));
}
fn freeShelves(self: &Self, from_count: ShelfIndex, to_count: ShelfIndex) void {