DRIVER-2651 recently added new BSON corpus tests for Decimal128 where the degenerate_extjson representation uses very large exponent values.

POC-ing these tests with PHPC resulted in several failures converting the degenerate extJSON to Canonical BSON. The code path in PHPC's test runner directly utilizes libbson's bson_new_from_json() function.

The spec tests and details of the PHPC failures can be found in mongodb/specifications#1432. matt.dale@mongodb.com's assessment from this #dbx-devs thread is as follows:

As far as the failures, the ones that failed with

-180000001364000000000000000000000000000000fe5f00
+180000001364000000000000000000000000000000000000

were expecting 0E+6111 but got 0E-6176.

The ones that failed with

-180000001364000000000000000000000000000000008000
+180000001364000000000000000000000000000000fedf00

were expecting 0E-6176 but got 0E+6111.

Seems like it could be some kind of exponent overflow/underflow problem.