similar: use cheaper hash() function to test exact matches We just need a hash table {fctx.data(): fctx} which doesn't keep fctx.data() in memory. Let's simply use hash(fctx.data()) to put data out from memory, and manage collided fctx objects by list. This isn't significantly faster than using sha1, but is more correct as we know SHA-1 collision attack is getting practical. Benchmark with 50k added/removed files, on tmpfs: $ hg addremove --dry-run --time -q previous: real 12.420 secs (user 11.120+0.000 sys 1.280+0.000) this patch: real 12.350 secs (user 11.210+0.000 sys 1.140+0.000)