RawImageDigest clarifications

Has anyone implemented RawImageDigest support (for DNG)? The spec is fairly straightforward, saying just the following:

"This tag is an MD5 digest of the raw image data. All pixels in the image are processed in row- scan order. Each pixel is zero padded to 16 or 32 bits deep (16-bit for data less than or equal to 16 bits deep, 32-bit otherwise). The data for each pixel is processed in little-endian byte order."

On reading this I was a little surprised that there is any processing needed on the raw pixel data - I supposed RawImageDigest was an md5 digest of unpadded, truly "raw" image data as it is stored in the DNG wrapper. Does anyone here have any insight into this? Are you aware of any free code libraries or command line tools which implement RawImageDigest calculations?

Thanks for any leads,

Roger Howard