read-bits.lisp

(defun read-bits (count &key (endian :be))
  (block outer
    (with-slots (buffer-size buffer-data) *bit-buffer*
      (let ((res 0))
        (loop
          with d = 0
          with i = 0
          when (= i count)
            do
               (return (values res i))
          if (< buffer-size 1)
            do
               (let ((new-byte (handler-case (read-integer :endian endian)
                                 (end-of-file () nil))))
                 (if new-byte
                     (progn
                       (setf buffer-size 8)
                       (setf buffer-data new-byte))
                     (return-from outer (values res i))))
          if (>= buffer-size 1)
            do
               (let ((bit (ldb (byte 1 (- buffer-size 1)) buffer-data)))
                 (setf res (+ bit (* 2 res)))
                 (setf (ldb (byte 1 (- buffer-size 1)) buffer-data) 0)
                 (decf buffer-size)
                 (incf i)))))))