Add implementation of exercise 3-30

Author: ramsayleung

README.org

@@ -25,7 +25,7 @@
   习题完成情况:
   - 章节一: 43/46
   - 章节二: 88/97
-  - 章节三: 29/82
+  - 章节三: 30/82
   - 章节四: TODO
   - 章节五: TODO
 * 运行

chapter3/adder.rkt

@@ -20,6 +20,8 @@
     (or-gate c1 c2 c-out))
   'ok)
 
+(provide half-adder full-adder)
+
 (module+ test
   (require rackunit)
 

chapter3/exercise3-30.rkt

@@ -0,0 +1,85 @@
+#lang racket
+(require "digital-circuit.rkt")
+(require "sicp-compat.rkt")
+(require "adder.rkt")
+(require "after-delay.rkt")
+
+;;; 延迟分析
+;;; 全加器延迟是 2 and-gate-delay + 1 or-gate delay
+;;; n位的级联进位加法器就是 n * (2 * and-gate-delay + or-gate-delay)
+(define (ripple-carry-adder a-list b-list s-list c-out)
+  (define (iter a-wires b-wires s-wires c-in)
+    (if (null? a-wires)
+        'done
+        (let ((a (car a-wires))
+              (b (car b-wires))
+              (s (car s-wires))
+              (next-carry (if (null? (cdr a-wires))
+                              c-out
+                              (make-wire))))
+          (full-adder a b c-in s next-carry)
+          (iter (cdr a-wires) (cdr b-wires) (cdr s-wires) next-carry))))
+  (let ((c-in (make-wire)))
+    (set-signal! c-in 0)
+    (iter a-list b-list s-list c-in)))
+
+(module+ test
+  (require rackunit)
+
+  (define (make-wire-list n)
+    (if (= n 0)
+        '()
+        (cons (make-wire) (make-wire-list (- n 1)))))
+
+  (define (get-wire-list-signal wires)
+    (if (null? wires)
+        '()
+        (cons (get-signal (car wires))
+              (get-wire-list-signal (cdr wires)))))
+
+  (define (set-wire-signals! wires values)
+    (if (or (null? wires) (null? values))
+        'done
+        (begin
+          (set-signal! (car wires) (car values))
+          (set-wire-signals! (cdr wires) (cdr values)))))
+
+  (test-case "Test for ripple-carry-adder, 5 + 3 = 8"
+             (let ((a-wires (make-wire-list 4))
+                   (b-wires (make-wire-list 4))
+                   (s-wires (make-wire-list 4))
+                   (c-wire (make-wire)))
+               (ripple-carry-adder a-wires b-wires s-wires c-wire)
+
+               ;; Using little-endian bit order (LSB first)
+               ;; 5 = 0101 in binary -> (1 0 1 0) in little-endian
+               ;; 3 = 0011 in binary -> (1 1 0 0) in little-endian
+               ;; 8 = 1000 in binary -> (0 0 0 1) in little-endian
+               (set-wire-signals! a-wires (list 1 0 1 0))
+               (set-wire-signals! b-wires (list 1 1 0 0))
+               (propagate)
+               (check-equal? (get-wire-list-signal s-wires) (list 0 0 0 1))
+               (check-equal? (get-signal c-wire) 0)
+               ))
+
+  (test-case "Test for ripple-carry-adder, 9 + 10 = 19"
+             (let ((a-wires (make-wire-list 4))
+                   (b-wires (make-wire-list 4))
+                   (s-wires (make-wire-list 4))
+                   (c-wire (make-wire)))
+               (ripple-carry-adder a-wires b-wires s-wires c-wire)
+
+               ;; Using little-endian bit order (LSB first)
+               ;; 9  = 1001 in binary -> (1 0 0 1) in little-endian
+               ;; 10 = 1010 in binary -> (0 1 0 1) in little-endian
+               ;; 19 = 10011 in binary -> (1 1 0 0 1) in little-endian
+               ;; 19 = 16 + 3 = 0b10000 + 0b0011
+               (set-wire-signals! a-wires (list 1 0 0 1))
+               (set-wire-signals! b-wires (list 0 1 0 1))
+               (propagate)
+               ;; 1 1 0 0 in little-endian
+               (check-equal? (get-wire-list-signal s-wires) (list 1 1 0 0))
+               ;; 0b10000
+               (check-equal? (get-signal c-wire) 1)
+               ))
+  )