What

Numbers are interleaved so that negative and positive numbers all share a positive space. For example the number line becomes this: 0, 1, -1, 2, -2, 3, -3, and so on

If a coding scheme does not support negative numbers but you need it to, this is what you use.

Why

Used by Protocol Buffers to store numbers which may be negative or positive.

• Protocol Buffers

I don't know why they use them though. CBOR and others just have a negative integer type which gets around having to encode the flag bit.

How

sint32: (n << 1) ^ (n >> 31)

sint64: (n << 1) ^ (n >> 63)

Second shift is arithmetic/circular. In Nim its easiest to pull in C code via emit.