> I see. IIUC from a brief re-reading of the code, saving that chunk would only save us from re-loading "parent->shift" from L1 cache and shifting the key. The cycles spent doing that seem small compared to the rest of the work involved in growing a node. Expressions like "if (idx < 0) return false;" return to an asserts-only variable, so in production builds, I would hope that branch gets elided (I haven't checked).
On further reflection, this is completely false and I'm not sure what I was thinking. However, for the update-inner case maybe we can assert that we found a valid slot.
