Optimize Varint encoding

bugadani commented 2 years ago

This PR optimizes the varint_* functions to avoid an unnecessary bit masking.

The idea behind this PR is the following:

Iteration stops if (value >>= 7) == 0, in which case value < 128. In this case, the 0x7F masking isn't necessary.
If value > 128 we want to set the highest bit of the extracted byte to 1. In this case, the 0x7F masking isn't necessary, because we overwrite the masked bit anyway.

Assuming I'm not catastrophically wrong, the resulting code optimizes slightly better: https://rust.godbolt.org/z/8dz48vocx

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jamesmunns commented 2 years ago

Looks great, thanks!

jamesmunns / postcard