From 7c6f69eb7a623782396075a1f126c2c665d704e4 Mon Sep 17 00:00:00 2001
From: Masaya Tojo <masaya@tojo.tokyo>
Date: Thu, 14 Jul 2022 00:11:44 +0900
Subject: Add huffman-encode.

---
 huffman-encode.lisp | 481 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 481 insertions(+)
 create mode 100644 huffman-encode.lisp

(limited to 'huffman-encode.lisp')

diff --git a/huffman-encode.lisp b/huffman-encode.lisp
new file mode 100644
index 0000000..eeaa38f
--- /dev/null
+++ b/huffman-encode.lisp
@@ -0,0 +1,481 @@
+;;; Provide Huffman encoding
+(in-package "ACL2")
+
+;;; Deine Huffman tree
+(defun nodep (x)
+  (declare (xargs :guard t))
+  (and (consp x)
+       (eq (car x) 'node)))
+
+(defun huffman-treep (x)
+  (declare (xargs :guard t))
+  (flet ((symbol-list (x)
+           (if (nodep x)
+               (second x)
+               (list (second x)))))
+    (if (nodep x)
+        (and (true-listp x)
+             (equal (len x) 5)
+             (true-listp (second x))
+             (rationalp (third x))
+             (huffman-treep (fourth x))
+             (huffman-treep (fifth x))
+             (equal (second x)
+                    (append (symbol-list (fourth x))
+                            (symbol-list (fifth x))))
+             (equal (third x)
+                    (+ (third (fourth x))
+                       (third (fifth x)))))
+        (and (true-listp x)
+             (equal (len x) 3)
+             (equal (first x) 'leaf)
+             (rationalp (third x))))))
+
+(defun huffman-leaf (s w)
+  (declare (xargs :guard (rationalp w)))
+  (list 'leaf s w))
+
+(defun huffman-leafp (x)
+  (declare (xargs :guard t))
+  (and (huffman-treep x)
+       (not (nodep x))))
+
+(defun leaf-symbol (x)
+  (declare (xargs :guard (and (huffman-treep x)
+                              (not (nodep x)))))
+  (second x))
+
+(defun symbol-list (x)
+  (declare (xargs :guard (huffman-treep x)))
+  (if (nodep x)
+      (second x)
+      (list (second x))))
+
+(defun weight (x)
+  (declare (xargs :guard (huffman-treep x)))
+  (third x))
+
+(defun left (x)
+  (declare (xargs :guard (and (huffman-treep x)
+                              (nodep x))))
+  (fourth x))
+
+(defun right (x)
+  (declare (xargs :guard (and (huffman-treep x)
+                              (nodep x))))
+  (fifth x))
+
+(defun huffman-node (l r)
+  (declare (xargs :guard (and (huffman-treep l)
+                              (huffman-treep r))))
+  (list 'node
+        (append (symbol-list l)
+                (symbol-list r))
+        (+ (weight l) (weight r))
+        l
+        r))
+
+(defthm huffman-leaf-elim
+  (implies (and (not (nodep x))
+                (huffman-treep x))
+           (equal (huffman-leaf (leaf-symbol x)
+                                (weight x))
+                  x))
+  :rule-classes :elim)
+
+(defthm len=5
+  (implies (true-listp x)
+           (equal (equal (len x) 5)
+                  (and (consp x)
+                       (consp (cdr x))
+                       (consp (cddr x))
+                       (consp (cdddr x))
+                       (consp (cddddr x))
+                       (null (cdr (cddddr x)))))))
+
+(defthm huffman-node-elim
+  (implies (and (nodep x)
+                (huffman-treep x))
+           (equal (huffman-node (left x) (right x))
+                  x))
+  :hints (("Goal" :use len=5
+                  :in-theory (disable len=5)))
+  :rule-classes :elim)
+
+(defun node-count (x)
+  (if (nodep x)
+      (+ 1
+         (node-count (left x))
+         (node-count (right x)))
+      0))
+
+(defthm node-count-left
+  (implies (nodep x)
+           (< (node-count (left x))
+              (node-count x)))
+  :rule-classes :linear)
+
+(defthm node-count-right
+  (implies (nodep x)
+           (< (node-count (right x))
+              (node-count x)))
+  :rule-classes :linear)
+
+(defthm huffman-treep-huffman-node
+  (implies (and (huffman-treep l)
+                (huffman-treep r))
+           (huffman-treep (huffman-node l r))))
+
+(defthm nodep-huffman-node
+  (implies (and (huffman-treep l)
+                (huffman-treep r))
+           (nodep (huffman-node l r))))
+
+(defthm symbol-list-left-right
+  (implies (and (nodep x)
+                (huffman-treep x))
+           (equal (symbol-list x)
+                  (append (symbol-list (left x))
+                          (symbol-list (right x))))))
+
+(defthm weight-left-right
+  (implies (and (nodep x)
+                (huffman-treep x))
+           (equal (weight x)
+                  (+ (weight (left x))
+                     (weight (right x))))))
+
+(defthm huffman-treep-left
+  (implies (and (nodep x)
+                (huffman-treep x))
+           (huffman-treep (left x))))
+
+(defthm huffman-treep-right
+  (implies (and (nodep x)
+                (huffman-treep x))
+           (huffman-treep (right x))))
+
+(defthm true-listp-symbol-list
+  (implies (huffman-treep x)
+           (true-listp (symbol-list x))))
+
+(defthm symbol-list-leaf
+  (implies (and (huffman-treep x)
+                (not (nodep x)))
+           (equal (symbol-list x)
+                  (list (leaf-symbol x)))))
+
+(defthm rationalp-weight
+  (implies (huffman-treep x)
+           (rationalp (weight x))))
+
+(defthm rationalp-weight-2
+  (implies (and (not (nodep (huffman-leaf lsl wt)))
+                (huffman-treep (huffman-leaf lsl wt)))
+           (rationalp wt)))
+
+(defthm huffman-treep-huffman-leaf
+  (implies (rationalp w)
+           (huffman-treep (huffman-leaf s w))))
+
+(in-theory (disable
+            nodep huffman-treep
+            leaf-symbol
+            huffman-leaf huffman-node
+            symbol-list weight left right
+            node-count))
+
+;;; Generate huffman trees
+(defun huffman-leaf-listp (x)
+  (declare (xargs :guard t))
+  (if (atom x)
+      (null x)
+      (and (huffman-treep (car x))
+           (not (nodep (car x)))
+           (huffman-leaf-listp (cdr x)))))
+
+(defun huffman-tree-listp (x)
+  (declare (xargs :guard t))
+  (if (atom x)
+      (null x)
+      (and (huffman-treep (car x))
+           (huffman-tree-listp (cdr x)))))
+
+(defun orderdp (x)
+  (declare (xargs :guard (huffman-tree-listp x)))
+  (cond ((atom x) t)
+        ((<= (weight (car x)) (weight (car x)))
+         (orderdp (cdr x)))
+        (t nil)))
+
+
+(defun symbol-weight-pair-listp (x)
+  (declare (xargs :guard t))
+  (if (atom x)
+      (null x)
+      (and (consp (car x))
+           (consp (cdar x))
+           (rationalp (cadar x))
+           (null (cddar x))
+           (symbol-weight-pair-listp (cdr x)))))
+
+
+(defun insert (e x)
+  (declare (xargs :guard (and (huffman-treep e)
+                              (huffman-tree-listp x))))
+  (cond ((endp x) (list e))
+        ((<= (weight e) (weight (car x)))
+         (cons e x))
+        (t
+         (cons (car x)
+               (insert e (cdr x))))))
+
+(defun generate (x a)
+  (declare (xargs :measure (len x)
+                  :guard (and (huffman-tree-listp x)
+                              (orderdp x)
+                              (huffman-treep a))))
+  (cond ((endp x) a)
+        ((<= (weight a) (weight (car x)))
+         (generate (cdr x) (huffman-node a (car x))))
+        ((endp (cdr x))
+         (huffman-node (car x) a))
+        ((<= (weight a) (weight (cadr x)))
+         (generate (cdr x)
+                   (huffman-node (car x) a)))
+        (t
+         (generate (insert a (cddr x))
+                   (huffman-node (car x) (cadr x))))))
+
+(defun pairs-to-leaves (x)
+  (declare (xargs :guard (symbol-weight-pair-listp x)))
+  (if (endp x)
+      nil
+      (insert (huffman-leaf (caar x) (cadar x))
+              (pairs-to-leaves (cdr x)))))
+
+(defun generate-huffman-tree (x)
+  (declare (xargs :guard (and (symbol-weight-pair-listp x)
+                              (< 1 (len x)))
+                  :verify-guards nil))
+  (let ((leaves (pairs-to-leaves x)))
+    (generate (cdr leaves) (car leaves))))
+
+(defun count-and-remove (e x)
+  (declare (xargs :guard (true-listp x)))
+  (cond ((endp x) (mv 0 nil))
+        ((equal e (car x))
+         (mv-let (c rest)
+             (count-and-remove e (cdr x))
+           (mv (+ 1 c) rest)))
+        (t
+         (mv-let (c rest)
+             (count-and-remove e (cdr x))
+           (mv c (cons (car x) rest))))))
+
+
+(defun message-to-pairs (x)
+  (declare (xargs :guard (true-listp x)))
+  (if (endp x)
+      nil
+      (mv-let (c rest)
+          (count-and-remove (car x) x)
+        (cons (list (car x) c)
+              (message-to-pairs rest)))))
+
+
+;;; Huffman encode/decode.
+(defun encode-1 (x tree)
+  (declare (xargs :guard (huffman-treep tree)
+                  :measure (node-count tree)))
+  (if (nodep tree)
+      (cond ((member-equal x (symbol-list (left tree)))
+             (cons 0 (encode-1 x (left tree))))
+            (t
+             (cons 1 (encode-1 x (right tree)))))
+      nil))
+
+(defun encode (x tree)
+  (declare (xargs :guard (and (true-listp x)
+                              (nodep tree)
+                              (huffman-treep tree))))
+  (if (endp x)
+      nil
+      (append (encode-1 (car x) tree)
+              (encode (cdr x) tree))))
+
+
+(defun bit-listp (x)
+  (declare (xargs :guard t))
+  (if (atom x)
+      (null x)
+      (and (bitp (car x))
+           (bit-listp (cdr x)))))
+
+(defun decode-1 (x tree)
+  (declare (xargs :guard (and (bit-listp x)
+                              (huffman-treep tree))
+                  :measure (node-count tree)))
+  (cond ((and (consp x) (nodep tree))
+         (if (equal (car x) 0)
+             (decode-1 (cdr x) (left tree))
+             (decode-1 (cdr x) (right tree))))
+        ((nodep tree) (mv nil nil))
+        (t
+         (mv (leaf-symbol tree) x))))
+
+(defun decode (x tree)
+  (declare (xargs :measure (len x)
+                  :guard (and (bit-listp x)
+                              (nodep tree)
+                              (huffman-treep tree))))
+  (if (or (endp x)
+          (not (nodep tree)))
+      nil
+      (mv-let (symbol rest)
+          (decode-1 x tree)
+        (cons symbol (decode rest tree)))))
+
+
+;;; --- defthm: pairs ---
+
+(defthm rationalp-0-count-and-remove
+  (rationalp (car (count-and-remove e x))))
+
+(defthm symbol-weight-pair-listp-message-to-pairs
+  (symbol-weight-pair-listp (message-to-pairs x)))
+
+;; --- insert - generate
+
+(defthm huffman-tree-listp-insert
+  (implies (and (huffman-tree-listp x)
+                (huffman-treep e))
+           (huffman-tree-listp (insert e x))))
+
+(defthm orderdp-insert
+  (implies (orderdp x)
+           (orderdp (insert e x))))
+
+(defthm huffman-tree-listp-pairs-to-leaves
+  (implies (symbol-weight-pair-listp x)
+           (huffman-tree-listp (pairs-to-leaves x))))
+
+(defthm orderdp-pairs-to-leaves
+  (orderdp (pairs-to-leaves x)))
+
+(defthm huffman-treep-generate
+  (implies (and (huffman-treep a)
+                (huffman-tree-listp x)
+                (consp x))
+           (huffman-treep (generate x a))))
+
+(defthm nodep-generate
+  (implies (and (huffman-treep a)
+                (huffman-tree-listp x)
+                (consp x))
+           (nodep (generate x a))))
+
+(defthm huffman-tree-listp-cdr
+  (implies (huffman-tree-listp x)
+           (huffman-tree-listp (cdr x))))
+
+(verify-guards generate-huffman-tree)
+
+(defthm huffman-treep-car
+  (implies (and (consp x) (huffman-tree-listp x))
+           (huffman-treep (car x))))
+
+(defthm len>1-consp
+  (equal (< 1 (len x))
+         (and (consp x)
+              (consp (cdr x)))))
+
+(defthm nodep-generate-huffman-tree
+  (implies (and (symbol-weight-pair-listp x)
+                (< 1 (len x)))
+           (nodep (generate-huffman-tree x))))
+
+(defthm huffman-treep-generate-huffman-tree
+  (implies (and (symbol-weight-pair-listp x)
+                (< 1 (len x)))
+           (huffman-treep (generate-huffman-tree x))))
+
+;;; ----- decode-encode
+(defthm bit-listp-encode-1
+  (bit-listp (encode-1 x tree)))
+
+(defthm bit-listp-encode
+  (bit-listp (encode x tree)))
+
+(defthm consp-append
+  (equal (consp (append x y))
+         (or (consp x)
+             (consp y))))
+
+(defthm consp-encode-1
+  (implies (and (member-equal x (symbol-list tree))
+                (huffman-treep tree)
+                (nodep tree))
+           (consp (encode-1 x tree))))
+
+(defthm consp-encode
+  (implies (and (consp x)
+                (true-listp x)
+                (huffman-treep tree)
+                (nodep tree)
+                (subsetp x (symbol-list tree)))
+           (consp (encode x tree))))
+
+
+(defthm len-decode-1
+  (implies (and (consp x)
+                (nodep tree))
+           (< (len (mv-nth 1 (decode-1 x tree)))
+              (len x))))
+  
+(defthm member-append
+  (iff (member-equal e (append x y))
+       (or (member-equal e x)
+           (member-equal e y))))
+
+(defthm decode-1-encode-1
+  (implies (and (huffman-treep tree)
+                (member-equal x (symbol-list tree)))
+           (and (equal (mv-nth 0 (decode-1 (encode-1 x tree) tree))
+                       x)
+                (equal (mv-nth 1 (decode-1 (encode-1 x tree) tree))
+                       nil))))
+
+(defthm decode1-append
+  (implies (and (huffman-treep tree)
+                (member-equal x (symbol-list tree)))
+           (and (equal (mv-nth 0 (decode-1 (append (encode-1 x tree)
+                                                      y)
+                                              tree))
+                       x)
+                (equal (mv-nth 1 (decode-1 (append (encode-1 x tree)
+                                                      y)
+                                              tree))
+                       y))))
+
+(defthm decode-encode-to-decode1-encode1
+  (implies (and (huffman-treep tree)
+                (nodep tree)
+                (member-equal x (symbol-list tree))
+                (subsetp y (symbol-list tree)))
+           (equal (decode (append (encode-1 x tree)
+                                          (encode y tree))
+                                  tree)
+                  (cons (mv-nth 0 (decode-1 (encode-1 x tree) tree))
+                        (decode (encode y tree)
+                                        tree))))
+  :hints (("Goal" :induct (decode x tree))))
+
+(defthm decode-encode
+  (implies (and (true-listp x)
+                (huffman-treep tree)
+                (nodep tree)
+                (subsetp x (symbol-list tree)))
+           (equal (decode (encode x tree)
+                                  tree)
+                  x)))
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