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no-allocation swap

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Folkert 2021-04-03 21:20:38 +02:00
parent 17b5dcb92a
commit 220c8b1a73
1 changed files with 60 additions and 28 deletions
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88
compiler/builtins/bitcode/src/list.zig
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@ -690,21 +690,46 @@ fn listRangeHelp(allocator: *Allocator, comptime T: type, low: T, high: T) RocLi
}
}
fn swap(source_ptr: [*]u8, element_width: usize, index_1: usize, index_2: usize) void {
const temp: [*]u8 = @ptrCast([*]u8, std.heap.c_allocator.alloc(u8, element_width) catch unreachable);
fn swap(source_ptr: [*]u8, element_width_initial: usize, index_1: usize, index_2: usize) void {
const threshold: comptime usize = 64;
const element_at_i = source_ptr + (index_1 * element_width);
const element_at_j = source_ptr + (index_2 * element_width);
// Store I Element in temp
@memcpy(temp, element_at_i, element_width);
var element_width = element_width_initial;
// Swap I Element with J Element
@memcpy(element_at_i, element_at_j, element_width);
var buffer_actual: [threshold]u8 = undefined;
var buffer: [*]u8 = buffer_actual[0..];
// Swap J Element with temp
@memcpy(element_at_j, temp, element_width);
var element_at_i = source_ptr + (index_1 * element_width);
var element_at_j = source_ptr + (index_2 * element_width);
std.heap.c_allocator.free(temp[0..element_width]);
while (true) {
if (element_width < threshold) {
// Store I Element in temp
@memcpy(buffer, element_at_i, element_width);
// Swap I Element with J Element
@memcpy(element_at_i, element_at_j, element_width);
// Swap J Element with buffer
@memcpy(element_at_j, buffer, element_width);
return;
} else {
// Store I Element in temp
@memcpy(buffer, element_at_i, threshold);
// Swap I Element with J Element
@memcpy(element_at_i, element_at_j, threshold);
// Swap J Element with buffer
@memcpy(element_at_j, buffer, threshold);
element_at_i += threshold;
element_at_j += threshold;
element_width -= threshold;
}
}
}
fn partition(source_ptr: [*]u8, transform: Opaque, wrapper: CompareFn, element_width: usize, low: isize, high: isize) isize {
@ -718,30 +743,37 @@ fn partition(source_ptr: [*]u8, transform: Opaque, wrapper: CompareFn, element_w
const ordering = wrapper(transform, current_elem, pivot);
const order = @intToEnum(utils.Ordering, ordering);
// If current element is smaller than the pivot
if (order == utils.Ordering.LT or order == utils.Ordering.EQ) {
i += 1; // increment index of smaller element
swap(source_ptr, element_width, @intCast(usize, i), @intCast(usize, j));
switch (order) {
utils.Ordering.LT, utils.Ordering.EQ => {
// the current element is smaller than the pivot; swap it
i += 1;
swap(source_ptr, element_width, @intCast(usize, i), @intCast(usize, j));
},
utils.Ordering.GT => {},
}
}
swap(source_ptr, element_width, @intCast(usize, i + 1), @intCast(usize, high));
return (i + 1);
}
fn quicksort(list: RocList, transform: Opaque, wrapper: CompareFn, element_width: usize, low: isize, high: isize) RocList {
if (list.bytes) |source_ptr| {
if (low < high) {
const pi = partition(source_ptr, transform, wrapper, element_width, low, high);
fn quicksort(source_ptr: [*]u8, transform: Opaque, wrapper: CompareFn, element_width: usize, low: isize, high: isize) void {
if (low < high) {
// partition index
const pi = partition(source_ptr, transform, wrapper, element_width, low, high);
const _unused1 = quicksort(list, transform, wrapper, element_width, low, pi - 1); // before pi
const _unused2 = quicksort(list, transform, wrapper, element_width, pi + 1, high); // after pi
}
const _unused1 = quicksort(source_ptr, transform, wrapper, element_width, low, pi - 1); // before pi
const _unused2 = quicksort(source_ptr, transform, wrapper, element_width, pi + 1, high); // after pi
}
}
pub fn listSortWith(input: RocList, transform: Opaque, wrapper: CompareFn, alignment: usize, element_width: usize) callconv(.C) RocList {
var list = input.makeUnique(std.heap.c_allocator, alignment, element_width);
if (list.bytes) |source_ptr| {
const low = 0;
const high: isize = @intCast(isize, list.len()) - 1;
quicksort(source_ptr, transform, wrapper, element_width, low, high);
}
return list;
}
pub fn listSortWith(list: RocList, transform: Opaque, wrapper: CompareFn, alignment: usize, element_width: usize) callconv(.C) RocList {
const low = 0;
const high: isize = @intCast(isize, list.len()) - 1;
return quicksort(list, transform, wrapper, element_width, low, high);
}