ruby/benchmark/bm_hash_shift_u24.rb

h = {}

(0xff4000..0xffffff).each do |i|
  h[i] = nil
end

300000.times do
  k, v = h.shift
  h[k] = v
end
hash.c (rb_num_hash_start): avoid pathological behavior The OR-ing itself is bad for a hash function, and shifting 3 bits left was not enough to undo the damage done by shifting (RUBY_SPECIAL_SHIFT+3) bits right. Experimentally, shifting 16-17 bits seemed to work well in preparing the number for murmur hash. Add a few more benchmarks to based on bm_hash_shift to ensure we don't hurt performance too much with tweaks. I'm pretty confident about this change and commiting it now; especially since we're still using Murmur behind it (but perhaps we can update to a newer hash from Murmur...) [ruby-core:72028] [Feature #11405] target 0: a (ruby 2.3.0dev (2015-12-11 trunk 53027) [x86_64-linux]) at "/home/ew/rrrr/b/ruby" target 1: b (ruby 2.3.0dev (2015-12-11 master 53027) [x86_64-linux]) at "/home/ew/ruby/b/ruby" benchmark results: minimum results in each 5 measurements. Execution time (sec) name a b hash_aref_dsym 0.279 0.276 hash_aref_dsym_long 4.951 4.936 hash_aref_fix 0.281 0.283 hash_aref_flo 0.060 0.060 hash_aref_miss 0.409 0.410 hash_aref_str 0.387 0.385 hash_aref_sym 0.275 0.270 hash_aref_sym_long 0.410 0.411 hash_flatten 0.252 0.237 hash_ident_flo 0.035 0.032 hash_ident_num 0.254 0.251 hash_ident_obj 0.252 0.256 hash_ident_str 0.250 0.252 hash_ident_sym 0.259 0.270 hash_keys 0.267 0.267 hash_shift 0.016 0.015 hash_shift_u16 0.074 0.072 hash_shift_u24 0.071 0.071 hash_shift_u32 0.073 0.072 hash_to_proc 0.008 0.008 hash_values 0.263 0.264 Speedup ratio: compare with the result of `a' (greater is better) name b hash_aref_dsym 1.009 hash_aref_dsym_long 1.003 hash_aref_fix 0.993 hash_aref_flo 1.001 hash_aref_miss 0.996 hash_aref_str 1.006 hash_aref_sym 1.017 hash_aref_sym_long 0.998 hash_flatten 1.061 hash_ident_flo 1.072 hash_ident_num 1.012 hash_ident_obj 0.987 hash_ident_str 0.993 hash_ident_sym 0.959 hash_keys 0.997 hash_shift 1.036 hash_shift_u16 1.039 hash_shift_u24 1.001 hash_shift_u32 1.017 hash_to_proc 1.001 hash_values 0.995 git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@53037 b2dd03c8-39d4-4d8f-98ff-823fe69b080e 2015-12-11 11:23:46 +03:00			`h = {}`

			`(0xff4000..0xffffff).each do \|i\|`
			`h[i] = nil`
			`end`

			`300000.times do`
			`k, v = h.shift`
			`h[k] = v`
			`end`