+ (logxor (ash (logand x (ash most-positive-fixnum -4)) 4)
+ (logand (ash x -1) most-positive-fixnum) ; to get sign bit into hash
+ 361475658)))
+
+;;; SXHASH of SIMPLE-BIT-VECTOR values is defined as a DEFTRANSFORM
+;;; because it is endian-dependent.
+(deftransform sxhash ((x) (simple-bit-vector))
+ `(let ((result 410823708))
+ (declare (type fixnum result))
+ (let ((length (length x)))
+ (cond
+ ((= length 0) (mix result (sxhash 0)))
+ (t
+ (mixf result (sxhash (length x)))
+ (do* ((i 0 (+ i 1))
+ ;; FIXME: should we respect DEPTHOID? SXHASH on
+ ;; strings doesn't seem to...
+ (end-1 (floor (1- length) sb!vm:n-word-bits)))
+ ((= i end-1)
+ (let ((num
+ (logand
+ (ash (1- (ash 1 (mod length sb!vm:n-word-bits)))
+ ,(ecase sb!c:*backend-byte-order*
+ (:little-endian 0)
+ (:big-endian
+ '(- sb!vm:n-word-bits
+ (mod length sb!vm:n-word-bits)))))
+ (%vector-raw-bits x i))))
+ (mix result ,(ecase sb!c:*backend-byte-order*
+ (:little-endian
+ '(logand num most-positive-fixnum))
+ (:big-endian
+ '(ash num (- sb!vm:n-lowtag-bits)))))))
+ (declare (type index i end-1))
+ (let ((num (%vector-raw-bits x i)))
+ (mixf result ,(ecase sb!c:*backend-byte-order*
+ (:little-endian
+ '(logand num most-positive-fixnum))
+ ;; FIXME: I'm not certain that
+ ;; N-LOWTAG-BITS is the clearest way of
+ ;; expressing this: it's essentially the
+ ;; difference between `(UNSIGNED-BYTE
+ ;; ,SB!VM:N-WORD-BITS) and (AND FIXNUM
+ ;; UNSIGNED-BYTE).
+ (:big-endian
+ '(ash num (- sb!vm:n-lowtag-bits))))))))))))