Remove the repeated logic of the method that overwrites the lower nibble of container type descriptor.

[linlin-s]

Issue #, if available:
N/A

Description of changes:

This PR optimize the process of overwriting lower nibble of type descriptor by avoid unnecessary method calls:

index = index(position)
offset = offset(position)

Context:

While writing containers, if the container length is small enough to fit in the lower nibble of the type descriptor byte, we will overwrite the lower nibble of the type descriptor byte with encoded length.

Before change, we need to use method buffer.getUInt8At () to calculate the OCTET of the type descriptor then combine it with the length value and then write the value to buffer by using buffer.writeVarUInt8At(). Both of these methods including calculations index = index(position), offset = offset(position). In this PR, we will pass the length value directly tobuffer.writeVarUInt8At()to avoid repeated calculations of index and offset.

Here are the benchmark results before and after changes:

Results from benchmarking a write of data equivalent to a stream of 194617 nested binary Ion value(3 forks, 2 warmups, 2 iterations, preallocation 1).

Benchmark	Before	After	Units
Bench.run	3919.464	3815.232	ms/op
Bench.run:Heap usage	3502.561	3311.067	MB
Bench.run:Serialized size	201.663	201.663	MB
Bench.run:·gc.alloc.rate	160.113	164.271	MB/sec
Bench.run:·gc.alloc.rate.norm	687893000.4	687857152.9	B/op
Bench.run:·gc.churn.G1_Eden_Space	15.839	20.501	MB/sec
Bench.run:·gc.churn.G1_Eden_Space.norm	68273948.44	85750215.11	B/op
Bench.run:·gc.churn.G1_Old_Gen	29.175	40.867	MB/sec
Bench.run:·gc.churn.G1_Old_Gen.norm	125954616.9	170904007.1	B/op
Bench.run:·gc.count	6	8	counts
Bench.run:·gc.time	216	233	ms

Results from benchmarking a write of data equivalent to a stream of 59155 nested binary Ion values(3 forks, 2 warmups, 2 iterations, preallocation 1).

Benchmark	Before	After	Units
Bench.run	504.162	490.292	ms/op
Bench.run:Heap usage	353.553	367.848	MB
Bench.run:Serialized size	21.271	21.271	MB
Bench.run:·gc.alloc.rate	126.217	129.877	MB/sec
Bench.run:·gc.alloc.rate.norm	70042252.14	70052759.49	B/op
Bench.run:·gc.churn.G1_Eden_Space	7.497	7.652	MB/sec
Bench.run:·gc.churn.G1_Eden_Space.norm	4161015.873	4127727.746	B/op
Bench.run:·gc.churn.G1_Old_Gen	144.318	147.497	MB/sec
Bench.run:·gc.churn.G1_Old_Gen.norm	80097528.48	79557871.75	B/op
Bench.run:·gc.churn.G1_Survivor_Space	0.307	0.224	MB/sec
Bench.run:·gc.churn.G1_Survivor_Space.norm	171300.86	120510.984	B/op
Bench.run:·gc.count	90	106	counts
Bench.run:·gc.time	599	695	ms

Results from benchmarking a write of data equivalent to a single nested binary Ion value(3 forks, 2 warmups, 2 iterations, preallocation 1).

Benchmark	Before	After	Units
Bench.run	0.087	0.082	ms/op
Bench.run:Heap usage	13.589	14.288	MB
Bench.run:Serialized size	0.005	0.005	MB
Bench.run:·gc.alloc.rate	90.841	96.427	MB/sec
Bench.run:·gc.alloc.rate.norm	8719.18	8697.858	B/op
Bench.run:·gc.churn.G1_Eden_Space	90.847	96.498	MB/sec
Bench.run:·gc.churn.G1_Eden_Space.norm	8719.42	8703.814	B/op
Bench.run:·gc.churn.G1_Survivor_Space	0.004	0.004	MB/sec
Bench.run:·gc.churn.G1_Survivor_Space.norm	0.385	0.342	B/op
Bench.run:·gc.count	443	473	counts
Bench.run:·gc.time	222	230	ms

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Files	Coverage Δ
...rc/com/amazon/ion/impl/bin/IonRawBinaryWriter.java	92.03% <100.00%> (-0.03%)	⬇️
src/com/amazon/ion/impl/bin/WriteBuffer.java	95.54% <100.00%> (+0.01%)	⬆️

... and 1 file with indirect coverage changes

📢 Thoughts on this report? Let us know!

[tgregg]

I suggest creating a new method (something like 'writeLowerNibbleAt'), and call it for this purpose, instead of branching within this method.

[tgregg]

Nice