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Predicate int64_zigzag_when/2
 int64_zigzag_when(?Original, ?Encoded) is det[private]
Convert between a signed integer value and its zigzag encoding, used for the protobuf sint32 and sint64 types. This is a low-level predicate; normally, you should use template_message/2 and the appropriate template term.

SWI-Prolog allows integer values greater than 64 bits, so a range check is done.

This predicate delays until either Original or Encoded is sufficiently instantiated.

There is also a non-delayed int64_zigzag/2

Original- an integer in the original form
Encoded- the zigzag encoding of Original
- Type,Domain if Original or Encoded are of the wrong type or out of range.
- instantiation error if both Original and Encoded are uninstantiated.
See also
- https://developers.google.com/protocol-buffers/docs/encoding#types