Remove appends.

src/SHA/SHA2.mo

@@ -1,4 +1,5 @@
 import Array "mo:base/Array";
+import Buffer "mo:base/Buffer";
 import Binary "mo:encoding/Binary";
 import Iter "mo:base/Iter";
 import Nat32 "mo:base/Nat32";
@@ -52,7 +53,15 @@ module {
         public func size() : Nat { hashSize; };
 
         public func sum(bs : [Nat8]) : [Nat8] {
-            Array.append(bs, checkSum());
+            let cs = checkSum();
+            let size = bs.size();
+            Array.tabulate<Nat8>(
+                size + cs.size(),
+                func (x : Nat) {
+                    if (x < size) return bs[x];
+                    cs[x - size];
+                }
+            );
         };
 
         public func checkSum() : [Nat8] {
@@ -71,12 +80,15 @@ module {
                 ));
             };
             write(Binary.BigEndian.fromNat64(n << 3));
-            var digest : [Nat8] = [];
+            let digest = Buffer.Buffer<Nat8>(32);
             label l for (i in h.keys()) {
                 if (i == 7 and hashSize == 28) { break l; };
-                digest := Array.append(digest, Binary.BigEndian.fromNat32(h[i]));
+                let n = Binary.BigEndian.fromNat32(h[i]);
+                for (v in n.vals()) {
+                    digest.add(v);
+                };
             };
-            digest;
+            digest.toArray();
         };
 
         public func write(bs : [Nat8]) : () {

src/Utilities.mo

@@ -9,8 +9,9 @@ module Utilities {
         src : [T],
     ) : Nat {
         let l = dst.size();
+        if (l < n) return 0;
         for (i in src.keys()) {
-            if (l <= i) return l;
+            if (l <= n + i) return l;
             dst[n + i] := src[i];
         };
         src.size();

test/SHA256.mo

@@ -2,8 +2,6 @@ import Blob "mo:base/Blob";
 import Hex "mo:encoding/Hex";
 import Text "mo:base/Text";
 
-import Debug "mo:base/Debug";
-
 import SHA256 "../src/SHA/SHA256";
 
 let sum256 = SHA256.sum(Blob.toArray(Text.encodeUtf8("hello world\n")));

vessel.dhall

@@ -1,4 +1,4 @@
 {
   dependencies = [ "base", "encoding" ],
-  compiler = Some "0.6.10"
+  compiler = Some "0.6.22"
 }