source: branches/f4grobner/fast-add.lisp@ 4437

(in-package :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))

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