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Update List.dropAt to no longer use Nat

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Richard Feldman 2024-01-22 23:37:27 -05:00
parent 4a870c8ee0
commit a8918a4e3b
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4 changed files with 17 additions and 12 deletions
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21
crates/compiler/builtins/bitcode/src/list.zig
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@ -698,28 +698,33 @@ pub fn listDropAt(
list: RocList,
alignment: u32,
element_width: usize,
drop_index: usize,
drop_index_u64: u64,
dec: Dec,
) callconv(.C) RocList {
const size = list.len();
const size_u64 = @as(u64, @intCast(size));
// If droping the first or last element, return a seamless slice.
// For simplicity, do this by calling listSublist.
// In the future, we can test if it is faster to manually inline the important parts here.
if (drop_index == 0) {
if (drop_index_u64 == 0) {
return listSublist(list, alignment, element_width, 1, size -| 1, dec);
} else if (drop_index == size -| 1) {
} else if (drop_index_u64 == size_u64 - 1) { // It's fine if (size - 1) wraps on size == 0 here,
// because if size is 0 then it's always fine for this branch to be taken; no
// matter what drop_index was, we're size == 0, so empty list will always be returned.
return listSublist(list, alignment, element_width, 0, size -| 1, dec);
}
if (list.bytes) |source_ptr| {
if (drop_index >= size) {
if (drop_index_u64 >= size_u64) {
return list;
}
if (drop_index < size) {
const element = source_ptr + drop_index * element_width;
dec(element);
}
// This cast must be lossless, because we would have just early-returned if drop_index
// were >= than `size`, and we know `size` fits in usize.
const drop_index = @as(usize, @intCast(drop_index_u64));
const element = source_ptr + drop_index * element_width;
dec(element);
// NOTE
// we need to return an empty list explicitly,