bug#66696: 29.1; "A bug in the function debug."

[Lewis Creary]

While I was trying to diagnose a bug in the function displayed just below

with the help of the function debug, the interim values of the lisp variables shown were inconsistent with the code being debugged.  For example, when called with the argument 5, the first element of the remainder list should be 1 (5 divided by 2 leaves a remainder of 1).  However, the fn debug claims that the variable `rmdr-list' has the first element 0.  This is just wrong!  And it has nothing to do with the problem being debugged.

(defun dec-to-bin (n)

  (let ((dividend n)

        (rmdr-list nil)

        (stop-sw nil)

        (numstr "") )

    (while ((and (>= dividend 0) (not stop-sw)))

       (setq dividend (/ dividend 2)

             rmdr-list (append (list (% dividend 2))                                               rmdr-list) )

       (if (= dividend 0)

           (setq stop-sw t)) )

       (debug) )

    (while rmdr-list

      (setq numstr (concat numstr (number-to-string                                          (car rmdr-list)))

            rmdr-list (cdr rmdr-list) ) )

    (string-to-number numstr) ))

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In GNU emacs 29.1 (build 2, x86_64-w64-mingw32) of 2023-08-02 built on

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