source: branches/f4grobner/integer-ring.lisp@ 4440

;;; -*-  Mode: Lisp -*- 
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;;;                                                                              
;;;  Copyright (C) 1999, 2002, 2009, 2015 Marek Rychlik <rychlik@u.arizona.edu>          
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;;;  This program is free software; you can redistribute it and/or modify        
;;;  it under the terms of the GNU General Public License as published by        
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;;;  GNU General Public License for more details.                                
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;;;  You should have received a copy of the GNU General Public License           
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(in-package "RING")

(defclass integer-ring (rational-field)
  ((value :initarg :value :initform 0 :accessor integer-ring-value :type integer))
  (:documentation "An object representing an integer.")
  )
           
(defmethod print-object ((self integer-ring) stream)
  (print-unreadable-object (self stream :type t :identity t)
    (with-accessors ((value integer-ring-value))
        self
      (format stream "VALUE=~A" value))))

(defmethod shared-initialize :around ((self integer-ring) slot-names 
                                      &rest initargs 
                                      &key (value nil value-supplied-p))
  "Checks the argument VALUE. Calls error if it is not an integer."
  (declare (ignore  initargs))
  (when value-supplied-p
    (assert (integerp value) nil "When initializing INTEGER-RING, argument VALUE must be an integer, got ~S." value))
  (call-next-method))


(defmethod unary-inverse ((self integer-ring))
  "Invert SELF, possibly changing class to RATIONAL-FIELD."
  (with-slots (value)
      self
    (case value
      (1 self)
      (-1 self)
      (t
       (warn "In UNARY-INVERSE with argument ~S, conversion from INTEGER-RING to RATIONAL-FIELD." self)
       (unary-inverse (change-class self 'rational-field))))))

(defmethod universal-gcd ((self integer-ring) (other integer-ring))
  (with-slots (value)
      self
    (with-slots ((other-value value))
        other
      (make-instance 'integer-ring :value (gcd value other-value)))))

(defmethod universal-ezgcd ((object integer-ring) (other integer-ring))
  (with-slots (value)
      object
    (with-slots ((other-value value))
        other
      (let ((c (gcd value other-value)))
        (values (make-instance 'integer-ring :value c)
                (make-instance 'integer-ring :value (/ value c))
                (make-instance 'integer-ring :value (/ other-value c)))))))