CodeKnight & CopyPaste
CodeKnight CodeKnight
CopyPaste CopyPaste
CodeKnight CodeKnight
I've been trying to find a more efficient way to represent large sparse matrices in memory. Any ideas on balancing compression with fast access?
CopyPaste CopyPaste
Hey, if you’re hunting for the sweet spot between compression and speed, give CSR or CSC a spin – they’re the OGs for row‑major or column‑major sweeps. If you can afford a bit of overhead, COO’s great for random inserts, then pack it into a compressed block format like BCSR or ELLPACK when you hit regular patterns. For really crazy sparsity, look at sparse hash tables or bit‑packed indices – they keep cache lines tight but can slow a single lookup a tad. Bottom line: keep the data layout friendly to your access pattern; a small cache‑friendly chunk often beats a monolithic compressed blob. Happy hacking!
CodeKnight CodeKnight
CSR is fine for linear scans, but I keep a little array of offsets to avoid the branch mispredictions you get when you walk a jagged row. For random lookups I actually hash the row/col pair, it hurts locality but makes the index O(1). The trick is to keep the dense chunks small so the cache can stay in line – I usually keep them 64 or 128 bytes. If you’re only reading, a bit‑packed index with SIMD can shave a lot off the latency, though you’ll pay in complexity. Anyway, I’ll try your BCSR idea next night. Happy hacking.
CopyPaste CopyPaste
Nice tricks – the offset hack really kills those branch penalties, and that hash lookup is classic over‑engineered fun. 64‑byte blocks are perfect for the L1, just keep an eye on padding. If you want to get even leaner, you could try a tiny Bloom filter on the hash to weed out misses before you hit the big table – saves a cycle or two. Go smash that BCSR tomorrow, let me know if it bites back!
CodeKnight CodeKnight
Nice, a Bloom filter will cut the false‑positive hits. Just make sure the false‑positive rate stays low enough that you’re not discarding useful indices. I’ll prototype the BCSR tomorrow, hit me up if the branchless offset scheme still outperforms the hash route. Happy coding.
CopyPaste CopyPaste
Sounds solid – just tune those hash buckets so you’re not chasing phantom indices. Keep the Bloom low‑bit and you’ll shave a cycle. Shoot me a ping when the BCSR starts dancing, I’ll be ready to debug any quirks. Happy coding!