source: branches/f4grobner/fast-add.lisp@ 4431

(load "boot")

(use-package :polynomial)
(use-package :monom)

;;(shadow '(fast-add) "POLYNOMIAL")

;; Getter/setter of leading coefficient
(defun lc (x) (term-coeff (car x)))
(defun (setf lc) (new-value x) (setf (term-coeff (car x)) new-value))

(defvar order-fn #'lex>)
(defvar add-fn #'add-to)

(defun fast-add-helper (p q)
  (do ((h p))
      ((endp q) p)
    (multiple-value-bind 
          (greater-p equal-p)
        (funcall order-fn (car h) (car q))
      (cond
        (greater-p                      ; (> (lm h) (lm q))
         (setf h (cdr h))
         )
        (equal-p                        ; (= (lm h) (lm q))
         (let ((s (funcall add-fn (lc h) (lc q))))
           (cond 
             ((universal-zerop s)
              (cond 
                (setf h (cdr h)
                      q (cdr q))))
             (t 
              ;; Adjust the lc of p
              (setf (lc h) s)
              (setf h (cdr h)
                       q (cdr q))))))

        (t                       ;(< (lm h) (lm q))