Write VarInt as fast as possible by unrolling the loop

[AkmalFairuz]

Description

VarInt is a hot path in the Minecraft Bedrock network protocol, so we need to make it as fast as possible. After some testing and benchmarking, I found that unrolling the loop makes VarInt writes faster. In most cases, we usually write 1-2-byte VarInts. For 2-byte VarInts, the speed is about the same, but for 1-byte VarInts it’s around 13% faster. As you can see from the benchmark results, writing VarInts of 3 bytes or more becomes significantly faster!.

Test & Benchmark Code: https://gist.github.com/AkmalFairuz/daadc682603ae5f1d0f77b7fd748853e
Inspired by: https://steinborn.me/posts/performance/how-fast-can-you-write-a-varint/

Benchmark Result

goos: darwin
goarch: arm64
pkg: varint-asap/asap
cpu: Apple M1 Pro
BenchmarkWriteVaruint64_Loop
BenchmarkWriteVaruint64_Loop/1B
BenchmarkWriteVaruint64_Loop/1B-2    	371880081	         3.066 ns/op
BenchmarkWriteVaruint64_Loop/2B
BenchmarkWriteVaruint64_Loop/2B-2    	275919524	         4.348 ns/op
BenchmarkWriteVaruint64_Loop/3B
BenchmarkWriteVaruint64_Loop/3B-2    	186233250	         6.439 ns/op
BenchmarkWriteVaruint64_Loop/4B
BenchmarkWriteVaruint64_Loop/4B-2    	139436500	         8.583 ns/op
BenchmarkWriteVaruint64_Loop/5B
BenchmarkWriteVaruint64_Loop/5B-2    	100000000	        10.71 ns/op
BenchmarkWriteVaruint64_Loop/6B
BenchmarkWriteVaruint64_Loop/6B-2    	93968712	        12.85 ns/op
BenchmarkWriteVaruint64_Loop/7B
BenchmarkWriteVaruint64_Loop/7B-2    	79125879	        14.97 ns/op
BenchmarkWriteVaruint64_Loop/8B
BenchmarkWriteVaruint64_Loop/8B-2    	69467226	        17.17 ns/op
BenchmarkWriteVaruint64_Loop/9B
BenchmarkWriteVaruint64_Loop/9B-2    	60143468	        19.27 ns/op
BenchmarkWriteVaruint64_Loop/10B
BenchmarkWriteVaruint64_Loop/10B-2   	55211548	        21.36 ns/op
BenchmarkWriteVaruint64_Unrolled
BenchmarkWriteVaruint64_Unrolled/1B
BenchmarkWriteVaruint64_Unrolled/1B-2         	452714943	         2.650 ns/op
BenchmarkWriteVaruint64_Unrolled/2B
BenchmarkWriteVaruint64_Unrolled/2B-2         	275627757	         4.349 ns/op
BenchmarkWriteVaruint64_Unrolled/3B
BenchmarkWriteVaruint64_Unrolled/3B-2         	240281890	         4.977 ns/op
BenchmarkWriteVaruint64_Unrolled/4B
BenchmarkWriteVaruint64_Unrolled/4B-2         	262098102	         4.588 ns/op
BenchmarkWriteVaruint64_Unrolled/5B
BenchmarkWriteVaruint64_Unrolled/5B-2         	249383619	         4.929 ns/op
BenchmarkWriteVaruint64_Unrolled/6B
BenchmarkWriteVaruint64_Unrolled/6B-2         	248166111	         4.807 ns/op
BenchmarkWriteVaruint64_Unrolled/7B
BenchmarkWriteVaruint64_Unrolled/7B-2         	235628038	         5.031 ns/op
BenchmarkWriteVaruint64_Unrolled/8B
BenchmarkWriteVaruint64_Unrolled/8B-2         	230897334	         5.175 ns/op
BenchmarkWriteVaruint64_Unrolled/9B
BenchmarkWriteVaruint64_Unrolled/9B-2         	223593786	         5.323 ns/op
BenchmarkWriteVaruint64_Unrolled/10B
BenchmarkWriteVaruint64_Unrolled/10B-2        	219333084	         5.450 ns/op
BenchmarkWriteVarint64_Loop
BenchmarkWriteVarint64_Loop/1B
BenchmarkWriteVarint64_Loop/1B-2              	392168236	         3.057 ns/op
BenchmarkWriteVarint64_Loop/2B
BenchmarkWriteVarint64_Loop/2B-2              	273143738	         4.371 ns/op
BenchmarkWriteVarint64_Loop/3B
BenchmarkWriteVarint64_Loop/3B-2              	184677511	         6.470 ns/op
BenchmarkWriteVarint64_Loop/4B
BenchmarkWriteVarint64_Loop/4B-2              	139671231	         8.567 ns/op
BenchmarkWriteVarint64_Loop/5B
BenchmarkWriteVarint64_Loop/5B-2              	100000000	        10.78 ns/op
BenchmarkWriteVarint64_Loop/6B
BenchmarkWriteVarint64_Loop/6B-2              	91436408	        12.91 ns/op
BenchmarkWriteVarint64_Loop/7B
BenchmarkWriteVarint64_Loop/7B-2              	78226857	        14.99 ns/op
BenchmarkWriteVarint64_Loop/8B
BenchmarkWriteVarint64_Loop/8B-2              	69691129	        17.07 ns/op
BenchmarkWriteVarint64_Loop/9B
BenchmarkWriteVarint64_Loop/9B-2              	61970401	        19.34 ns/op
BenchmarkWriteVarint64_Loop/10B
BenchmarkWriteVarint64_Loop/10B-2             	55047448	        21.39 ns/op
BenchmarkWriteVarint64_Unrolled
BenchmarkWriteVarint64_Unrolled/1B
BenchmarkWriteVarint64_Unrolled/1B-2          	445155319	         2.664 ns/op
BenchmarkWriteVarint64_Unrolled/2B
BenchmarkWriteVarint64_Unrolled/2B-2          	274548861	         4.350 ns/op
BenchmarkWriteVarint64_Unrolled/3B
BenchmarkWriteVarint64_Unrolled/3B-2          	247848409	         4.822 ns/op
BenchmarkWriteVarint64_Unrolled/4B
BenchmarkWriteVarint64_Unrolled/4B-2          	256862097	         4.706 ns/op
BenchmarkWriteVarint64_Unrolled/5B
BenchmarkWriteVarint64_Unrolled/5B-2          	257703038	         4.622 ns/op
BenchmarkWriteVarint64_Unrolled/6B
BenchmarkWriteVarint64_Unrolled/6B-2          	244516525	         4.869 ns/op
BenchmarkWriteVarint64_Unrolled/7B
BenchmarkWriteVarint64_Unrolled/7B-2          	238123762	         5.013 ns/op
BenchmarkWriteVarint64_Unrolled/8B
BenchmarkWriteVarint64_Unrolled/8B-2          	224577495	         5.326 ns/op
BenchmarkWriteVarint64_Unrolled/9B
BenchmarkWriteVarint64_Unrolled/9B-2          	217174342	         5.481 ns/op
BenchmarkWriteVarint64_Unrolled/10B
BenchmarkWriteVarint64_Unrolled/10B-2         	211523164	         5.636 ns/op
BenchmarkWriteVaruint32_Loop
BenchmarkWriteVaruint32_Loop/1B
BenchmarkWriteVaruint32_Loop/1B-2             	394702759	         3.035 ns/op
BenchmarkWriteVaruint32_Loop/2B
BenchmarkWriteVaruint32_Loop/2B-2             	274779033	         4.390 ns/op
BenchmarkWriteVaruint32_Loop/3B
BenchmarkWriteVaruint32_Loop/3B-2             	184443898	         6.480 ns/op
BenchmarkWriteVaruint32_Loop/4B
BenchmarkWriteVaruint32_Loop/4B-2             	139482516	         8.579 ns/op
BenchmarkWriteVaruint32_Loop/5B
BenchmarkWriteVaruint32_Loop/5B-2             	100000000	        10.74 ns/op
BenchmarkWriteVaruint32_Unrolled
BenchmarkWriteVaruint32_Unrolled/1B
BenchmarkWriteVaruint32_Unrolled/1B-2         	444092460	         2.689 ns/op
BenchmarkWriteVaruint32_Unrolled/2B
BenchmarkWriteVaruint32_Unrolled/2B-2         	273265885	         4.378 ns/op
BenchmarkWriteVaruint32_Unrolled/3B
BenchmarkWriteVaruint32_Unrolled/3B-2         	234322006	         5.001 ns/op
BenchmarkWriteVaruint32_Unrolled/4B
BenchmarkWriteVaruint32_Unrolled/4B-2         	260303686	         4.548 ns/op
BenchmarkWriteVaruint32_Unrolled/5B
BenchmarkWriteVaruint32_Unrolled/5B-2         	251496226	         4.894 ns/op
BenchmarkWriteVarint32_Loop
BenchmarkWriteVarint32_Loop/1B
BenchmarkWriteVarint32_Loop/1B-2              	392076781	         3.037 ns/op
BenchmarkWriteVarint32_Loop/2B
BenchmarkWriteVarint32_Loop/2B-2              	272029398	         4.389 ns/op
BenchmarkWriteVarint32_Loop/3B
BenchmarkWriteVarint32_Loop/3B-2              	184441194	         6.516 ns/op
BenchmarkWriteVarint32_Loop/4B
BenchmarkWriteVarint32_Loop/4B-2              	139376882	         8.583 ns/op
BenchmarkWriteVarint32_Loop/5B
BenchmarkWriteVarint32_Loop/5B-2              	100000000	        10.78 ns/op
BenchmarkWriteVarint32_Unrolled
BenchmarkWriteVarint32_Unrolled/1B
BenchmarkWriteVarint32_Unrolled/1B-2          	441986576	         2.717 ns/op
BenchmarkWriteVarint32_Unrolled/2B
BenchmarkWriteVarint32_Unrolled/2B-2          	272128358	         4.409 ns/op
BenchmarkWriteVarint32_Unrolled/3B
BenchmarkWriteVarint32_Unrolled/3B-2          	245919234	         4.926 ns/op
BenchmarkWriteVarint32_Unrolled/4B
BenchmarkWriteVarint32_Unrolled/4B-2          	265668538	         4.511 ns/op
BenchmarkWriteVarint32_Unrolled/5B
BenchmarkWriteVarint32_Unrolled/5B-2          	261839175	         4.620 ns/op
PASS