On Mon, 4 Sep 2023 12:20:52 GMT, Martin Doerr <mdo...@openjdk.org> wrote:
>> Sorry for the delay, I've been on vacation.
>
>> Sorry for the delay, I've been on vacation.
>
> No problem. Hope you had a good time! Thanks for your feedback.
@TheRealMDoerr We've been discussing the shifts in order to wrap our heads
around it, and we've ended up with this diagram in order to try and visualize
what happens:
Let's say we have a struct with 3 ints:
struct Foo {
int x;
int y;
int z;
};
If this struct is passed as an argument, then the load of the second 'half' of
the struct would look like this:
offset : 0 .... 32 ..... 64 ..... 96 .... 128
values : xxxxxxxx|yyyyyyyy|zzzzzzzz|???????? (can't touch bits
96..128)
Load int : V +--------+
| |
+--------+ |
V V
In register : ????????|zzzzzzzz (MSBs are 0)
Shift left : zzzzzzzz|00000000 (LSBs are zero)
Write long : V V
Result : xxxxxxxx|yyyyyyyy|zzzzzzzz|00000000
So, the 'Result' is padded at the tail with zeros.
Does that seem right? Does it seem useful to add this diagram as a comment
somewhere, for us when we come back to this code a year from now? Thanks
-------------
PR Comment: https://git.openjdk.org/jdk/pull/15417#issuecomment-1705350592
