I doubt you're going to get a nice clean answer. Chances are it's
"whatever Sanjay was thinking at the time" which led to the current
encoding, maintained throughout the proto versions for backwards
compatibility with existing data. While APIs have changed over time,
the wire encoding has remained
What is the rationale behind the current variable-width integer encoding?
As I understand it, an integer is terminated by a byte that's most-significant
bit is equal to zero. Thus, bytes must be read one at a time, and this
condition must be checked after reading each one to determine whether
