From: Ramakrishnan Muthukrishnan Date: Wed, 23 Mar 2011 16:26:08 +0000 (+0530) Subject: solutions to 3.28, 3.29 and 3.30 X-Git-Url: https://git.rkrishnan.org/%5B/%5D%20/uri/flags/status?a=commitdiff_plain;h=7bea10031060aeb9ca3ca716d301a1d02fb0f52e;p=sicp.git solutions to 3.28, 3.29 and 3.30 --- diff --git a/src/sicp/ex3_28.rkt b/src/sicp/ex3_28.rkt new file mode 100644 index 0000000..33e64b8 --- /dev/null +++ b/src/sicp/ex3_28.rkt @@ -0,0 +1,21 @@ +#lang racket + +(define (or-gate o1 o2 output) + (define (or-action-procedure) + (let ((new-value + (logical-or (get-signal o1) + (get-signal o2)))) + (after-delay or-gate-delay + (lambda () + (set-signal! output new-value))))) + + (define (logicval-or o1 o2) + (cond + ((and (= o1 0) (= o1 0)) 0) + ((or (= o1 1) (= o2 1)) 1) + (else (error "invalid signals")))) + + (add-action! o1 or-action-procedure) + (add-action! o2 or-action-procedure) + 'ok) + diff --git a/src/sicp/ex3_29.rkt b/src/sicp/ex3_29.rkt new file mode 100644 index 0000000..5d56596 --- /dev/null +++ b/src/sicp/ex3_29.rkt @@ -0,0 +1,25 @@ +#lang racket + +#| +(or a b) = (and (and (not a) b) + (and a (not b)) +|# + +(define (or-gate o1 o2 output) + (let ((a1 (make-wire)) + (a2 (make-wire)) + (a3 (make-wire)) + (a4 (make-wire))) + (inverter o1 a1) + (inverter o2 a2) + (and-gate a1 o2 a3) + (and-gate o1 a2 a4) + (and-gate a3 a4 output) + 'ok)) + +#| + +or-gate delay is one inverter delay + 2 x and-gate-delay, considering that +the whole things works in a parallel way. i.e. a3 and a4 are produced parallely. + +|# \ No newline at end of file diff --git a/src/sicp/ex3_30.rkt b/src/sicp/ex3_30.rkt new file mode 100644 index 0000000..f234752 --- /dev/null +++ b/src/sicp/ex3_30.rkt @@ -0,0 +1,67 @@ +#lang racket + +(define (half-adder a b s c) + (let ((d (make-wire)) (e (make-wire))) + (or-gate a b d) + (and-gate a b c) + (inverter c e) + (and-gate d e s) + 'ok)) + +(define (full-adder a b c-in sum c-out) + (let ((s (make-wire)) + (c1 (make-wire)) + (c2 (make-wire))) + (half-adder b c-in s c1) + (half-adder a s sum c2) + (or-gate c1 c2 c-out) + 'ok)) + +(define (last coll) + (cond + ((not (null? coll)) (error "coll not a list")) + ((null? (cdr coll)) (car coll)) + (else (last (cdr coll))))) + +(define (butlast coll) + (cond + ((not (null? coll)) (error "coll not a list")) + ((null? (cdr coll)) '()) + (else (cons (car coll) + (butlast (cdr coll)))))) + +(define (ripple-carry-adder a-list b-list s-list c) + (define (ripple-carry-adder-1 a-list b-list c-in s-list c-out) + (if (null? a-list) + 'ok + (begin + (full-adder (last a-list) + (last b-list) + c-in + (last s-list) + c-out) + (ripple-carry-adder-1 (butlast a-list) + (butlast b-list) + c-out + (butlast s-list) + c-out)))) + (let ((c-in (make-wire)) + (c-out (make-wire))) + (set-signal! c-in 0) + (ripple-carry-adder-1 a-list + b-list + c-in + s-list + c-out))) + +#| + +delay for s(n) = n x full-adder-delay + +1 full-adder-delay = 2 x half-adder-delay + 1 x or-gate-delay + +1 half-adder-delay = max ((and-gate-delay + inverter delay), or-gate-delay) + + and-gate-delay + +|# +