A complete SHA-1 name is shorter than max_hash_len, so it missed the full-width fast path and fell to the O(store) hex scan -- once per file under `ls --size` and `ls --long`. On tcl's tip the 545 SHA-1 named files cost ~54ms each against ~0.2ms for the 1,653 SHA3 ones.

The directory is ordered by raw digest, so a prefix's matches form one contiguous run. A binary search for the run plus a walk of it proves uniqueness rather than assuming it, which is what the SHA-1 case was surrendered to the scan for. Odd-length prefixes end mid-byte and keep the scan.

ls --size on tcl: 1.98s -> 0.03s. Issue #148. closed check-in: 4829f043b1 user: dmestas tags: fix-148-prefix-lookup