On Fri, May 2, 2025 at 6:31 PM Joaquin M López Muñoz via Boost < boost@lists.boost.org> wrote:
El 02/05/2025 a las 3:05, Ivan Matek via Boost escribió:
On Fri, May 2, 2025 at 2:10 AM Jean-Louis Leroy via Boost < boost@lists.boost.org> wrote:
Maybe Joaquín wants to jump in, I don't want to put words in his mouth ;-)
Would be nice, from what I got from his talk some performance I have seen in my experiments, e.g. finding perfect hash for 368 items in 512 buckets seems almost impossible when we apply formula from the talk.
To sum up, fast_perfect_hash::hash_initialize works against theoretical expectation because type_info objects in a program occupy a small, contiguous range of addresses within the memory space.
Joaquin M Lopez Munoz
Thank you, this matches what I have observed, but my knowledge of math was not good enough to go from fact that those values are similar and spaced evenly, e.g. one run on my machine: type_id: 0x445878 type_id: 0x4458a0 type_id: 0x4458c8 type_id: 0x4458f0 type_id: 0x445918 type_id: 0x445940 type_id: 0x445968 type_id: 0x445990 type_id: 0x4459b8 type_id: 0x4459e0 type_id: 0x445a08 type_id: 0x445a30 type_id: 0x445a58 ... to the fact that makes them easier to perfectly hash. Intuitively makes sense, but I could not find anything definitive. Thank you for explaining this and confirming my assumption.