; RTL - A Formal Theory of Register-Transfer Logic and Computer Arithmetic 
; Copyright (C) 1995-2013 Advanced Mirco Devices, Inc. 
;
; Contact:
;   David Russinoff
;   1106 W 9th St., Austin, TX 78703
;   http://www.russsinoff.com/
;
; 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 the Free Software
; Foundation; either version 2 of the License, or (at your option) any later
; version.
;
; This program is distributed in the hope that it will be useful but WITHOUT ANY
; WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
; PARTICULAR PURPOSE.  See the GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License along with
; this program; see the file "gpl.txt" in this directory.  If not, write to the
; Free Software Foundation, Inc., 51 Franklin Street, Suite 500, Boston, MA
; 02110-1335, USA.
;
; Author: David M. Russinoff (david@russinoff.com)

(in-package "ACL2")

(set-enforce-redundancy t)

(include-book "round")

(local (include-book "add-proofs"))

(set-inhibit-warnings "theory") ; avoid warning in the next event
(local (in-theory nil))



;;;**********************************************************************
;;;                      Bit Vector Addition
;;;**********************************************************************

(defthm half-adder
  (implies (and (bvecp u 1)
                (bvecp v 1))
           (equal (+ u v)
                  (cat (logand u v) 1 (logxor u v) 1)))
  :rule-classes ())

(defthm add-2
    (implies (and (natp x) (natp y))
	     (equal (+ x y)
		    (+ (logxor x y)
		       (* 2 (logand x y)))))
  :rule-classes ())

(defthm full-adder
  (implies (and (bvecp u 1)
                (bvecp v 1)
                (bvecp w 1))
           (equal (+ u v w)
                  (cat (logior (logand u v) (logior (logand u w) (logand v w))) 1 
                       (logxor u (logxor v w)) 1)))
  :rule-classes ())

(defthm add-3
    (implies (and (natp x)
		  (natp y)
		  (natp z))
	     (= (+ x y z)
		(+ (logxor x (logxor y z))
		   (* 2 (logior (logand x y)
				(logior (logand x z)
					(logand y z)))))))
  :rule-classes ())

(defun rc-carry (x y k)
  (if (zp k)
      0
    (logior (logand (bitn x (1- k)) (bitn y (1- k)))
	    (logior (logand (bitn x (1- k)) (rc-carry x y (1- k)))
		    (logand (bitn y (1- k)) (rc-carry x y (1- k)))))))

(defun rc-sum (x y k)
  (if (zp k)
      0
    (cat (logxor (bitn x (1- k))
		 (logxor (bitn y (1- k)) (rc-carry x y (1- k))))
	 1
	 (rc-sum x y (1- k))
	 (1- k))))

(defthm ripple-carry
  (implies (and (natp x)
                (natp y)
                (natp n))
           (equal (+ (bits x (1- n) 0) (bits y (1- n) 0))
                  (cat (rc-carry x y n) 1 (rc-sum x y n) n)))
  :rule-classes ())

(defun gen (x y i j)
  (declare (xargs :measure (nfix (1+ i))))
  (if (and (natp i) (natp j) (>= i j))
      (if (= (bitn x i) (bitn y i))
	  (bitn x i)
	(gen x y (1- i) j))
    0))

(defun prop (x y i j)
  (declare (xargs :measure (nfix (1+ i))))
  (if (and (natp i) (natp j) (>= i j))
      (if (= (bitn x i) (bitn y i))
	  0
	(prop x y (1- i) j))
    1))

(defthm bvecp-1-gen
  (bvecp (gen x y i j) 1)
  :rule-classes (:rewrite
                 (:forward-chaining :trigger-terms ((gen x y i j)))))

(defthm bvecp-1-prop
  (bvecp (prop x y i j) 1)
  :rule-classes (:rewrite
                 (:forward-chaining :trigger-terms ((prop x y i j)))))

(defthmd gen-val
  (implies (and (natp j) (>= i j))
           (equal (gen x y i j)
                  (if (>= (+ (bits x i j) (bits y i j))
                          (expt 2 (1+ (- i j))))
                      1
                    0))))

(defthmd gen-val-cor1
  (implies (natp j)
           (equal (gen x y i j)
                  (bitn (+ (bits x i j) (bits y i j))
			(1+ (- i j))))))

(defthmd gen-val-cor2
  (implies (and (natp x)
                (natp y)
		(natp i))
           (equal (+ (bits x i 0) (bits y i 0))
		  (+ (* (expt 2 (1+ i)) (gen x y i 0))
		     (bits (+ x y) i 0)))))

(defthm gen-special-case
  (implies (and (integerp i)
                (integerp j)
                (>= i j)
                (>= j 0)
                (= (bitn (+ (bits x i j) (bits y i j)) (- i j)) 0))
           (equal (gen x y i j)
                  (logior (bitn x i) (bitn y i))))
  :rule-classes ())

(defthmd prop-val
  (implies (and (integerp i) (natp j) (>= i j))
           (equal (prop x y i j)
                  (if (= (+ (bits x i j) (bits y i j))
                         (1- (expt 2 (1+ (- i j)))))
                      1
                    0))))

(defthmd prop-as-logxor
  (implies (and (natp i)
                (natp j)
                (<= j i)
                (natp x)
                (natp y))
           (equal (prop x y i j)
                  (if (equal (logxor (bits x i j) (bits y i j))
                             (1- (expt 2 (1+ (- i j)))))
                      1
                    0))))

(defthm gen-extend
    (implies (and (integerp i)
		  (integerp j)
		  (integerp k)
		  (> i k)
		  (>= k j)
		  (>= j 0))
	     (equal (gen x y i j)
		    (logior (gen x y i (1+ k))
			    (logand (prop x y i (1+ k))
				    (gen x y k j)))))
  :rule-classes ())

(defthm gen-extend-cor
  (implies (and (natp x)
                (natp y)
                (natp i)
                (natp j)
                (natp k)
                (> i k)
                (>= k j))
           (equal (gen x y i j)
                  (bitn (+ (bits x i (1+ k))
                           (bits y i (1+ k))
                           (gen x y k j))
                        (- i k))))
  :rule-classes ())

(defthm prop-extend
    (implies (and (integerp i)
		  (integerp j)
		  (integerp k)
		  (> i k)
		  (>= k j)
		  (>= j 0))
	     (equal (prop x y i j)
		    (logand (prop x y i (1+ k))
			    (prop x y k j))))
  :rule-classes ())

(defthm bits-sum
  (implies (and (integerp x) (integerp y))
           (equal (bits (+ x y) i j)
                  (bits (+ (bits x i j)
                           (bits y i j)
                           (gen x y (1- j) 0))
                        (- i j) 0)))
  :rule-classes ())

(defthmd bits-sum-swallow
  (implies (and (equal (bitn x k) 0)
                (natp x)
                (natp y)
                (integerp i)
                (integerp j)
                (integerp k)
                (>= i j)
                (> j k)
                (>= k 0)
                (<= y (expt 2 k)))
           (equal (bits (+ x y) i j)
                  (bits x i j))))

(defthmd bits-sum-cor
  (implies (and (integerp x)
                (integerp y)
                (>= i j)
                (>= j 0)
                (= (gen x y i j) 0)
                (= (gen x y (1- j) 0) 0))
           (equal (bits (+ x y) i j)
                  (+ (bits x i j) (bits y i j)))))

(defthm bits-sum-3
  (implies (and (integerp x) (integerp y) (integerp z))
           (equal (bits (+ x y z) i j)
                  (bits (+ (bits x i j)
                           (bits y i j)
                           (bits z i j)
                           (gen x y (1- j) 0)
                           (gen (+ x y) z (1- j) 0))
                        (- i j) 0)))
  :rule-classes ())

(defthm bits-sum-plus-1
    (implies (and (integerp x)
		  (integerp y)
		  (integerp i)
		  (integerp j)
		  (>= i j)
		  (>= j 0))
	     (equal (bits (+ 1 x y) i j)
		    (bits (+ (bits x i j)
			     (bits y i j)
			     (logior (prop x y (1- j) 0) 
				     (gen x y (1- j) 0) ))
			  (- i j) 0)))
  :rule-classes ())

(defthmd logand-gen-0
  (implies (and (integerp i)
                (integerp j)
                (>= i j)
                (>= j 0)
                (= (logand (bits x i j) (bits y i j)) 0))
           (equal (gen x y i j) 0)))


(defthm logand-gen-0-cor
  (implies (and (integerp x)
                (integerp y)
                (integerp i)
                (integerp j)
                (>= i j)
                (>= j 0)
                (= (logand x y) 0))
           (equal (bits (+ x y) i j)
                  (+ (bits x i j) (bits y i j))))
  :rule-classes ())

(defthmd gen-plus
  (implies (and (natp x)
                (natp y)
		(natp k)
		(bvecp z (1+ k))
		(= (logand z y) 0)
		(= (gen x y k 0) 1))
	   (equal (gen (+ x y) z k 0) 0)))

(defthmd gen-extend-3
    (implies (and (natp i)
		  (natp j)
		  (> i j)
		  (natp x)
		  (natp y)
		  (bvecp z (1+ j))
		  (= (logand y z) 0))		  
	     (equal (gen (+ x y) z i 0)
		    (logand (prop x y i (1+ j))
			    (gen (+ x y) z j 0)))))


;;;**********************************************************************
;;;                  Leading One Prediction
;;;**********************************************************************

(defund lop (a b d k)
  (let ((c (- (bitn a (1- k)) (bitn b (1- k)))))
    (if (and (integerp k) (>= k 0))
	(if (= k 0)
	    0
	  (if (= d 0)
	      (lop a b c (1- k))
	    (if (= d (- c))
		(lop a b (- c) (1- k))
	      k)))
      0)))

(defthm lop-bnds
  (implies (and (integerp a)
                (integerp b)
                (integerp n)
                (>= a 0)
                (>= b 0)
                (>= n 0)
                (not (= a b))
                (< a (expt 2 n))
                (< b (expt 2 n)))
           (or (= (lop a b 0 n) (expo (- a b)))
               (= (lop a b 0 n) (1+ (expo (- a b))))))
  :rule-classes ())

(defthm lop-thm-1
    (implies (and (integerp a)
		  (> a 0)
		  (integerp b)
		  (> b 0)
		  (= e (expo a))
		  (< (expo b) e)
		  (= lambda
		     (logior (* 2 (mod a (expt 2 e)))
			     (bits (lognot (* 2 b)) e 0))))
	     (or (= (expo (- a b)) (expo lambda))
		 (= (expo (- a b)) (1- (expo lambda)))))
  :rule-classes ())

(defun lamt (a b e)
  (logxor a (bits (lognot b) e 0)))

(defun lamg (a b e)
  (logand a (bits (lognot b) e 0)))

(defun lamz (a b e)
  (bits (lognot (logior a (bits (lognot b) e 0))) e 0))

(defun lam1 (a b e)
  (logand (bits (lamt a b e) e 2) 
	  (logand (bits (lamg a b e) (1- e) 1)
		  (bits (lognot (lamz a b e)) (- e 2) 0))))

(defun lam2 (a b e)
  (logand (bits (lognot (lamt a b e)) e 2)
	  (logand (bits (lamz a b e) (1- e) 1)
		  (bits (lognot (lamz a b e)) (- e 2) 0))))

(defun lam3 (a b e)
  (logand (bits (lamt a b e) e 2) 
	  (logand (bits (lamz a b e) (1- e) 1)
		  (bits (lognot (lamg a b e)) (- e 2) 0))))

(defun lam4 (a b e)
  (logand (bits (lognot (lamt a b e)) e 2)
	  (logand (bits (lamg a b e) (1- e) 1)
		  (bits (lognot (lamg a b e)) (- e 2) 0))))

(defun lam0 (a b e)
  (logior (lam1 a b e)
	  (logior (lam2 a b e)
		  (logior (lam3 a b e)
			  (lam4 a b e)))))

(defun lamb (a b e)
  (+ (* 2 (lam0 a b e))
     (bitn (lognot(lamt a b e)) 0)))

(defthm lop-thm-2
    (implies (and (integerp a)
		  (> a 0)
		  (integerp b)
		  (> b 0)
		  (not (= a b))
		  (= e (expo a))
		  (= e (expo b))
		  (> e 1))
	     (and (not (= (lamb a b e) 0))
		  (or (= (expo (- a b)) (expo (lamb a b e)))
		      (= (expo (- a b)) (1- (expo (lamb a b e)))))))
  :rule-classes ())


;;;**********************************************************************
;;;                    Trailing One Prediction
;;;**********************************************************************

(defthm top-thm-1
  (implies (and (natp n)
                (natp k)
                (< k n)
                (integerp a)
                (integerp b))
           (equal (equal (bits (+ a b 1) k 0) 0)
		  (equal (bits (lognot (logxor a b)) k 0) 0)))
  :rule-classes ())

(defthm top-thm-2
  (implies (and (natp n)
                (integerp a)
                (integerp b)
                (natp k)
                (< k n)
                (or (equal c 0) (equal c 1)))
           (equal (equal (bits (+ a b c) k 0) 0)
                  (equal (bits (logxor (logxor a b) 
                                       (cat (logior a b) n c 1))
                               k 0) 
                         0)))
  :rule-classes ())
