Reduce calls to Source#buffer(StringScanner#rest)

[naitoh]

Reduce calls to Source#buffer(StringScanner#rest)

Why

Source#buffer calling StringScanner#rest.
StringScanner#rest is slow.
Reduce calls to Source#buffer.

Benchmark

RUBYLIB= BUNDLER_ORIG_RUBYLIB= /Users/naitoh/.rbenv/versions/3.3.0/bin/ruby -v -S benchmark-driver /Users/naitoh/ghq/github.com/naitoh/rexml/benchmark/parse.yaml
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [arm64-darwin22]
Calculating -------------------------------------
                         before       after  before(YJIT)  after(YJIT)
                 dom     10.639      10.985        16.213       16.221 i/s -     100.000 times in 9.399033s 9.103461s 6.167962s 6.164794s
                 sax     28.357      29.440        42.900       44.375 i/s -     100.000 times in 3.526479s 3.396688s 2.331024s 2.253511s
                pull     32.852      34.210        48.976       51.273 i/s -     100.000 times in 3.043965s 2.923140s 2.041816s 1.950344s
              stream     30.821      31.908        43.953       44.697 i/s -     100.000 times in 3.244539s 3.134020s 2.275172s 2.237310s

Comparison:
                              dom
         after(YJIT):        16.2 i/s
        before(YJIT):        16.2 i/s - 1.00x  slower
               after:        11.0 i/s - 1.48x  slower
              before:        10.6 i/s - 1.52x  slower

                              sax
         after(YJIT):        44.4 i/s
        before(YJIT):        42.9 i/s - 1.03x  slower
               after:        29.4 i/s - 1.51x  slower
              before:        28.4 i/s - 1.56x  slower

                             pull
         after(YJIT):        51.3 i/s
        before(YJIT):        49.0 i/s - 1.05x  slower
               after:        34.2 i/s - 1.50x  slower
              before:        32.9 i/s - 1.56x  slower

                           stream
         after(YJIT):        44.7 i/s
        before(YJIT):        44.0 i/s - 1.02x  slower
               after:        31.9 i/s - 1.40x  slower
              before:        30.8 i/s - 1.45x  slower

• YJIT=ON : 1.00x - 1.05x faster
• YJIT=OFF : 1.03x - 1.04x faster

[kou]

I think that this is not a pattern. Can we use more suitable name such as buffer and next_data?

Can we remove [0,2]? I think that it's a needless method call.

[naitoh]

OK.
I see.

[kou]

We may want to reduce one more @source.buffer call.

pattern = @source.buffer
if pattern.size < 2
  @source.read
  pattern = @source.buffer
end

[naitoh]

It worked with this content.
Thank you!

[kou]

Thanks!

[naitoh]

Thanks!