Rust: Changes to `u128`/`i128` layout in 1.77 and 1.78

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A new Rust blog post/announcement has been posted!

Rust has long had an inconsistency with C regarding the alignment of 128-bit integers on the x86-32 and x86-64 architectures. This problem has recently been resolved, but the fix comes with some effects that are worth being aware of.

As a user, you most likely do not need to worry about these changes unless you are:

1. Assuming the alignment of i128/u128 rather than using align_of
2. Ignoring the improper_ctypes* lints and using these types in FFI

There are also no changes to architectures other than x86-32 and x86-64. If your code makes heavy use of 128-bit integers, you may notice runtime performance increases at a possible cost of additional memory use.

This post documents what the problem was, what changed to fix it, and what to expect with the changes. If you are already familiar with the problem and only looking for a compatibility matrix, jump to the Com...

Get the full details here: Changes to `u128`/`i128` layout in 1.77 and 1.78 | Rust Blog