Hey folks,
I’m generating some lookup tables at comptime, and wanted to look at storing this data more compactly, thought using PackedIntArray at comptime would be a good choice.
I’m hitting an error using packed structs with a backing integer type of u10. Repro case is below:
const std = @import("std");
const LookupTable = std.PackedIntArray(u10, 256);
fn makeLookupTable() LookupTable {
@setEvalBranchQuota(10_0000);
var table: LookupTable = undefined;
for (0..256) |i| {
table.set(i, @truncate(i));
}
return table;
}
const lookupTable = makeLookupTable();
export fn example() void {
_ = lookupTable.get(0);
}
This gives the following error using 0.11 (and trunk): error: comptime dereference requires 'packed_int_array.PackedIntArrayEndian(u10,.Little,256)' to have a well-defined layout, but it does not.
Changing the type to u9 makes this case compile fine. Any tips on why using u10 is not “well-defined” during comptime? Thanks!
(Interestingly u10, u11 and u12 all fail this way, but u1-u9 and u13-u16 are fine!)