What is the algorithm to compute the Amazon-S3 Etag for a file larger than 5GB

Question

Files uploaded to Amazon S3 that are smaller than 5GB have an ETag that is simply the MD5 hash of the file, which makes it easy to check if your local files are the same as what you put on S3.

But if your file is larger than 5GB, then Amazon computes the ETag differently.

For example, I did a multipart upload of a 5,970,150,664 byte file in 380 parts. Now S3 shows it to have an ETag of 6bcf86bed8807b8e78f0fc6e0a53079d-380. My local file has an md5 hash of 702242d3703818ddefe6bf7da2bed757. I think the number after the dash is the number of parts in the multipart upload.

I also suspect that the new ETag is still an MD5 hash, but with some metadata included along the way from the multipart upload somehow.

Does anyone know how to compute the ETag using the same algorithm as Amazon S3? Any help will be appreciated!!