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feat(bitcode): implement the unique case for List.reverse

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rvcas 2021-04-03 08:09:29 -04:00
parent ed47f288f7
commit 22d8659215
1 changed files with 37 additions and 9 deletions
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46
compiler/builtins/bitcode/src/list.zig
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@ -125,19 +125,47 @@ pub fn listReverse(list: RocList, alignment: usize, element_width: usize) callco
var i: usize = 0;
var end: usize = size - 1;
const output = RocList.allocate(std.heap.c_allocator, alignment, size, element_width);
if (list.isUnique()) {
const temp: [*]u8 = @ptrCast([*]u8, std.heap.c_allocator.alloc(u8, element_width) catch unreachable);
const target_ptr = output.bytes orelse unreachable;
// Working from the front and back so
// we only need to go ~(n / 2) iterations.
// If the length is an odd number the middle
// element stays in the same place anyways.
while (i < (end - i)) : (i += 1) {
const last_position = end - i;
while (i < size) : (i += 1) {
const source_position = end - i;
const last_element = source_ptr + (last_position * element_width);
const first_element = source_ptr + (i * element_width);
@memcpy(target_ptr + (i * element_width), source_ptr + (source_position * element_width), element_width);
// Store Last Element in temp
@memcpy(temp, last_element, element_width);
// Swap Last Element with First Element
@memcpy(last_element, first_element, element_width);
// Swap First Element with temp
@memcpy(first_element, temp, element_width);
}
std.heap.c_allocator.free(temp[0..element_width]);
return list;
} else {
const output = RocList.allocate(std.heap.c_allocator, alignment, size, element_width);
const target_ptr = output.bytes orelse unreachable;
while (i < size) : (i += 1) {
const last_position = end - i;
@memcpy(target_ptr + (i * element_width), source_ptr + (last_position * element_width), element_width);
}
utils.decref(std.heap.c_allocator, alignment, list.bytes, size * element_width);
return output;
}
utils.decref(std.heap.c_allocator, alignment, list.bytes, size * element_width);
return output;
} else {
return RocList.empty();
}