This comment is very useful but still refers to the C implementation.
Adapting it for Go is fairly straightforward though.

Change-Id: Ib6dde25f3a18acbce76bb3cffdc29f5ccf43c1f7
Reviewed-on: https://go-review.googlesource.com/41696Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>