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haberman | 5 months ago

I advocated for PrefixVarint (which seems equivalent to vint64 ) for WebAssembly, but it was decided against, in favor of LEB128: https://github.com/WebAssembly/design/issues/601

The recent CREL format for ELF also uses the more established LEB128: https://news.ycombinator.com/item?id=41222021

At this point I don't feel like I have a clear opinion about whether PrefixVarint is worth it, compared with LEB128.

discuss

order

zigzag312|5 months ago

Just remember that XML was more established than JSON for a long time.

kannanvijayan|5 months ago

Varint encoding is something I've peeked at in various contexts. My personal bias is towards the prefix-style, as it feels faster to decode and the segregation of the meta-data from the payload data is nice.

But, the thing that tends to tip the scales is the fact that in almost all real world cases, small numbers dominate - as the github thread you linked relates in a comment.

The LEB128 fast-path is a single conditional with no data-dependencies:

  if ! (x & 0x80) { x }
Modern CPUs will characterize that branch really well and you'll pay almost zero cost for the fastpath which also happens to be the dominant path.

It's hard to beat.