CPython uses this function.
Change-Id: I03ead7f54ad19e2a0b2ea3b142298cc1e55c3c90
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/53967
Auto-Submit: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>