From 37f3fabc6e699622320c7baa2b7e9b4c466d1c82 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Sat, 9 Nov 2024 13:03:36 -0500
Subject: base64: Factorize memoization.

---
 chickadee/base64.scm | 41 +++++++++++++++++++++--------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/chickadee/base64.scm b/chickadee/base64.scm
index c12fa39..9397f9f 100644
--- a/chickadee/base64.scm
+++ b/chickadee/base64.scm
@@ -41,16 +41,21 @@
             (lp (1+ i) (cdr chars)))))
       (error "invalid base64 alphabet" alphabet)))
 
-(define alphabet->decoder
-  (let ((cache (make-hash-table)))
-    (lambda (alphabet)
-      (or (hash-ref cache alphabet)
-          (let ((bv (make-bytevector 128 -1)))
-            (alphabet-for-each (lambda (i x)
-                                 (bytevector-s8-set! bv x i))
-                               alphabet)
-            (hash-set! cache alphabet bv)
-            bv)))))
+(define-syntax-rule (define/memoize1 (name arg) body ...)
+  (define name
+    (let ((cache (make-hash-table)))
+      (lambda (arg)
+        (or (hash-ref cache arg)
+            (let ((val (begin body ...)))
+              (hash-set! cache arg val)
+              val))))))
+
+(define/memoize1 (alphabet->decoder alphabet)
+  (let ((bv (make-bytevector 128 -1)))
+    (alphabet-for-each (lambda (i x)
+                         (bytevector-s8-set! bv x i))
+                       alphabet)
+    bv))
 
 (define* (base64-decode str #:optional (alphabet base64-alphabet))
   "Decode the base64 encoded string @var{str} using @var{alphabet} and
@@ -96,16 +101,12 @@ return a bytevector containing the decoded data."
                    (put-u8 out (logand x #x0000ff))
                    (lp))))))))))))
 
-(define alphabet->encoder
-  (let ((cache (make-hash-table)))
-    (lambda (alphabet)
-      (or (hash-ref cache alphabet)
-          (let ((bv (make-bytevector 64)))
-            (alphabet-for-each (lambda (i x)
-                                 (bytevector-u8-set! bv i x))
-                               alphabet)
-            (hash-set! cache alphabet bv)
-            bv)))))
+(define/memoize1 (alphabet->encoder alphabet)
+  (let ((bv (make-bytevector 64)))
+    (alphabet-for-each (lambda (i x)
+                         (bytevector-u8-set! bv i x))
+                       alphabet)
+    bv))
 
 (define* (base64-encode bv #:optional (alphabet base64-alphabet))
   "Encode the bytevector @var{bv} to a base64 using
-- 
cgit v1.2.3