Data commit

Task/Base64-decode-data/Ol/base64-decode-data.ol

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+(define base64-codes "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
+(define kernel (alist->ff (map cons (string->bytes base64-codes) (iota (string-length base64-codes)))))
+
+; returns n bits from input binary stream
+(define (bits n hold)
+   (let loop ((hold hold))
+      (vector-apply hold (lambda (v i l)
+         (cond
+            ((null? l)
+               (values (>> v (- i n)) #false))
+            ((pair? l)
+               (if (not (less? i n))
+                  (values (>> v (- i n)) (vector (band v (- (<< 1 (- i n)) 1)) (- i n) l))
+                  (loop (vector
+                     (bor (<< v 6) (kernel (car l) 0))
+                     (+ i 6)
+                     (unless (eq? (car l) "=") (cdr l))))))
+            (else
+               (loop (vector v i (l)))))))))
+
+; decoder.
+(define (decode str)
+   (print "decoding string '" str "':")
+   (let loop ((hold [0 0 (str-iter str)]))
+      (let*((bit hold (bits 8 hold)))
+         (unless (zero? bit) (display (string bit)))
+         (when hold
+            (loop hold))))
+   (print)(print))
+
+; TESTING
+(decode "SGVsbG8sIExpc3Ah")
+
+(decode "VG8gZXJyIGlzIGh1bWFuLCBidXQgdG8gcmVhbGx5IGZvdWwgdGhpbmdzIHVwIHlvdSBuZWVkIGEgY29tcHV0ZXIuCiAgICAtLSBQYXVsIFIuIEVocmxpY2g=")
+
+(decode "TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ1dCBieSB0aGlzIHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBhIGx1c3Qgb2YgdGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY29udGludWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25vd2xlZGdlLCBleGNlZWRzIHRoZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4=")