empty_hash_shortcut.diff

466c466
<     if (!st_lookup(RHASH(hash)->tbl, key, &val)) {
---
>     if (RHASH(hash)->tbl->num_entries == 0 || !st_lookup(RHASH(hash)->tbl, key, &val)) {

hash_benchmark.rb

require 'benchmark'

test = lambda do |n|
  lambda do
    h = {}
    h2 = {"a"=>"b"}
    10_000.times do |y|
      str = "a" * n
      sym = str.intern
      100.times do
        h[str]
        h[sym]
        h2[str]
        h2[sym]
      end
    end
  end
end

Benchmark.bm do |b|
  7.times do |n|
    b.report("#{1<<n}x", &test.call(1<<n))
  end
end

lourens_p248.txt

      user     system      total        real
1x  1.750000   0.010000   1.760000 (  1.759984)
2x  1.830000   0.000000   1.830000 (  1.828848)
4x  1.840000   0.000000   1.840000 (  1.847043)
8x  1.840000   0.010000   1.850000 (  1.843167)
16x  1.840000   0.000000   1.840000 (  1.848768)
32x  1.850000   0.000000   1.850000 (  1.849023)
64x  1.850000   0.010000   1.860000 (  1.857963)

sds_and_lourens_p248.txt

      user     system      total        real
1x  1.680000   0.000000   1.680000 (  1.688379)
2x  1.780000   0.010000   1.790000 (  1.777302)
4x  1.780000   0.000000   1.780000 (  1.783551)
8x  1.770000   0.000000   1.770000 (  1.780911)
16x  1.790000   0.010000   1.800000 (  1.786330)
32x  1.780000   0.000000   1.780000 (  1.790252)
64x  1.800000   0.000000   1.800000 (  1.800255)

sds_p248.txt

      user     system      total        real
1x  1.630000   0.000000   1.630000 (  1.636553)
2x  1.740000   0.000000   1.740000 (  1.735722)
4x  1.740000   0.010000   1.750000 (  1.740702)
8x  1.750000   0.000000   1.750000 (  1.760334)
16x  1.770000   0.000000   1.770000 (  1.775435)
32x  1.840000   0.010000   1.850000 (  1.835240)
64x  1.920000   0.000000   1.920000 (  1.933402)

Vanilla_ruby_p248.txt

      user     system      total        real
1x  1.690000   0.000000   1.690000 (  1.690578)
2x  1.770000   0.010000   1.780000 (  1.780384)
4x  1.800000   0.000000   1.800000 (  1.796044)
8x  1.830000   0.000000   1.830000 (  1.835327)
16x  1.860000   0.010000   1.870000 (  1.866744)
32x  1.950000   0.000000   1.950000 (  1.951703)
64x  2.110000   0.000000   2.110000 (  2.117919)