--- a
+++ b/contrib/sb-rotate-byte/compiler.lisp
@@ -0,0 +1,56 @@
+(in-package "SB-ROTATE-BYTE")
+
+(defknown rotate-byte (integer byte-specifier integer) integer
+  (foldable flushable))
+(defknown %rotate-byte (integer bit-index bit-index integer) integer
+  (foldable flushable))
+(defknown %unsigned-32-rotate-byte ((integer -31 31) (unsigned-byte 32))
+    (unsigned-byte 32)
+  (foldable flushable))
+
+(macrolet (;; see src/compiler/srctran.lisp
+           (with-byte-specifier ((size-var pos-var spec) &body body)
+             (once-only ((spec `(macroexpand ,spec))
+                         (temp '(gensym)))
+                        `(if (and (consp ,spec)
+                                  (eq (car ,spec) 'byte)
+                                  (= (length ,spec) 3))
+                        (let ((,size-var (second ,spec))
+                              (,pos-var (third ,spec)))
+                          ,@body)
+                        (let ((,size-var `(byte-size ,,temp))
+                              (,pos-var `(byte-position ,,temp)))
+                          `(let ((,,temp ,,spec))
+                             ,,@body))))))
+  (define-source-transform rotate-byte (count spec num)
+    (with-byte-specifier (size pos spec)
+      `(%rotate-byte ,count ,size ,pos ,num))))
+
+(defoptimizer (%rotate-byte derive-type) ((count size posn num))
+  ;; FIXME: this looks fairly unwieldy.  I'm sure it can be made
+  ;; simpler, and also be made to deal with negative integers too.
+  (let ((size (sb-c::continuation-type size)))
+    (if (numeric-type-p size)
+	(let ((size-high (numeric-type-high size))
+	      (num-type (sb-c::continuation-type num)))
+	  (if (and size-high
+		   num-type
+		   (<= size-high sb-vm:n-word-bits)
+		   (csubtypep num-type
+			      (specifier-type `(unsigned-byte ,size-high))))
+              (specifier-type `(unsigned-byte ,size-high))
+	      *universal-type*))
+        *universal-type*)))
+
+(deftransform %rotate-byte ((count size pos integer)
+			    ((constant-arg (member 0)) * * *) *)
+  "fold identity operation"
+  'integer)
+
+(deftransform %rotate-byte ((count size pos integer)
+			    ((or (integer -31 -1) (integer 1 31))
+			     (constant-arg (member 32))
+			     (constant-arg (member 0))
+			     (unsigned-byte 32)) *)
+  "inline 32-bit rotation"
+  '(%unsigned-32-rotate-byte count integer))