/*
* Calculate the checksum of data that is 16 byte aligned and a multiple of
* 16 bytes.
*
* The first step is to reduce it to 1024 bits. We do this in 8 parallel
* chunks in order to mask the latency of the vpmsum instructions. If we
* have more than 32 kB of data to checksum we repeat this step multiple
* times, passing in the previous 1024 bits.
*
* The next step is to reduce the 1024 bits to 64 bits. This step adds
* 32 bits of 0s to the end - this matches what a CRC does. We just
* calculate constants that land the data in this 32 bits.
*
* We then use fixed point Barrett reduction to compute a mod n over GF(2)
* for n = CRC using POWER8 instructions. We use x = 32.
*
* http://en.wikipedia.org/wiki/Barrett_reduction
*
* Copyright (C) 2015 Anton Blanchard <anton@au.ibm.com>, IBM
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of th
