contrib/sb-rotate-byte/rotate-byte.lisp

   1 (in-package "SB-ROTATE-BYTE")
   2
   3 (defun rotate-byte (count bytespec integer)
   4   "Rotates a field of bits within INTEGER; specifically, returns an
   5 integer that contains the bits of INTEGER rotated COUNT times
   6 leftwards within the byte specified by BYTESPEC, and elsewhere
   7 contains the bits of INTEGER."
   8   (rotate-byte count bytespec integer))
   9
  10 (defun %rotate-byte (count size pos integer)
  11   (let ((count (nth-value 1 (round count size)))
  12         (mask (1- (ash 1 size))))
  13     (logior (logand integer (lognot (ash mask pos)))
  14             (let ((field (logand (ash mask pos) integer)))
  15               (logand (ash mask pos)
  16                       (if (> count 0)
  17                           (logior (ash field count)
  18                                   (ash field (- count size)))
  19                           (logior (ash field count)
  20                                   (ash field (+ count size)))))))))
  21
  22 (defun %unsigned-32-rotate-byte (count integer)
  23   ;; inhibit transforms
  24   (declare (notinline %rotate-byte))
  25   (%rotate-byte count 32 0 integer))