Recently, Casey Muratori has implemented a proof-of-concept terminal, which is designed around fast input processing and rendering. This is an important and commendable effort, since the vast majority of software performs tens to thousands of times slower than it can.
One of the design choices of refterm is to use a hash table to cache glyph rendering. The key in this table is the UTF-8 string of a single glyph. To avoid string allocations, the hash value of the glyph bytes is used as a key instead.
When Casey got asked about the possibility of hash collisions on stream, he responded with a claim that the hash function used in refterm is “a strong hash”, and the complexity to find collision is about 2^64 operations. After analyzing the code for the hash function used in refterm, a few flaws were found in the hash function, and O(1) attacks were discovered.