Good question! It turns out that 64 bit arithmetic does not overflow (I explain this in a comment in the source code [1]) up to the shift. The shift amount must then be large enough to fit the result in 32 (or actually, 24 or usually 16) bits. For a valid FLAC file this will be the case. For an invalid FLAC file it might truncate, but an invalid file cannot be decoded properly anyway. The shift amount is a 5 bit signed number [2], so it is never possible to shift by the integer width or more.

[1]: https://github.com/ruuda/claxon/blob/91b6af9/src/subframe.rs... [2]: https://github.com/ruuda/claxon/blob/91b6af9/src/subframe.rs...