The definition of fxif reads in part "It can be implemented as (fxior (fxand (fxnot mask) i) (fxand mask j))." It should read "It can be implemented as (fxior (fxand mask i) (fxand (fxnot mask) j)))."  Please fix this as a post-finalization erratum.  The implementation and tests are already correct.  Thanks to Jim Rees for pointing this out.(fxrotate-bit-field i start end (+ count (- start end)))