3741 zfs needs better comments
Submitted by:   Will Andrews <willa@spectralogic.com>
Submitted by:   Justin Gibbs <justing@spectralogic.com>
Submitted by:   Alan Somers <alans@spectralogic.com>
Reviewed by:    Matthew Ahrens <mahrens@delphix.com>

*** 123,132 ****
--- 123,143 ----
   *
   * For both cached and uncached data, both fletcher checksums are much faster
   * than sha-256, and slower than 'off', which doesn't touch the data at all.
   */
  
+ /*
+  * TODO: vectorize these functions
+  * All of these functions are written so that each iteration of the loop
+  * depends on the value of the previous iteration.  Also, in the fletcher_4
+  * functions, each statement of the loop body depends on the previous
+  * statement.  These dependencies prevent the compiler from vectorizing the
+  * code to take advantage of SIMD extensions (unless GCC is far smarter than I
+  * think).  It would be easy to rewrite the loops to be amenable to
+  * autovectorization.
+  */
+ 
  #include <sys/types.h>
  #include <sys/sysmacros.h>
  #include <sys/byteorder.h>
  #include <sys/zio.h>
  #include <sys/spa.h>