Add initialization function to permit computation of SHA-224 hashes.

SHA-224 uses the exact same computation as SHA-256, just with different initial values.

sha256.asm

@@ -94,13 +94,56 @@ k private
 	dc i4'$90befffa, $a4506ceb, $bef9a3f7, $c67178f2'
 	end
 
-* Initialize a SHA-256 context.
+* Initialize a context for SHA-256 computation.
-* This must be called before any of the other SHA-256 functions.
+* An init function must be called before any of the other SHA-256 functions.
 sha256_init start
 	CFunction SHA256_INIT
 	end
 
-SHA256_INIT start
+* Initialize a context for SHA-224 computation.
+* To compute a SHA-224 hash, call this function, and then call the below
+* functions as if computing a SHA-256 hash. After calling sha256_finalize,
+* the first 28 bytes of context->hash will contain the SHA-224 hash.
+sha224_init start
+	CFunction SHA224_INIT
+	end
+
+SHA224_INIT start
+	lda	#$9ed8
+	sta	h0
+	lda	#$c105
+	sta	h0+2
+	lda	#$d507
+	sta	h1
+	lda	#$367c
+	sta	h1+2
+	lda	#$dd17
+	sta	h2
+	lda	#$3070
+	sta	h2+2
+	lda	#$5939
+	sta	h3
+	lda	#$f70e
+	sta	h3+2
+	lda	#$0b31
+	sta	h4
+	lda	#$ffc0
+	sta	h4+2
+	lda	#$1511
+	sta	h5
+	lda	#$6858
+	sta	h5+2
+	lda	#$8fa7
+	sta	h6
+	lda	#$64f9
+	sta	h6+2
+	lda	#$4fa4
+	sta	h7
+	lda	#$befa
+	sta	h7+2
+	bra	initdp
+
+SHA256_INIT entry
 	lda	#$e667
 	sta	h0
 	lda	#$6a09
@@ -134,7 +177,7 @@ SHA256_INIT start
 	lda	#$5be0
 	sta	h7+2
 
-	stz	length
+initdp	stz	length
 	stz	length+2
 	stz	length+4
 	stz	length+6

sha256.h

@@ -29,11 +29,19 @@ struct sha256_context {
  */
 
 /*
- * Initialize a SHA-256 context.
+ * Initialize a context for SHA-256 computation.
- * This must be called before any of the other SHA-256 functions.
+ * An init function must be called before any of the other SHA-256 functions.
  */
 void sha256_init(struct sha256_context *context);
 
+/*
+ * Initialize a context for SHA-224 computation.
+ * To compute a SHA-224 hash, call this function, and then call the below
+ * functions as if computing a SHA-256 hash. After calling sha256_finalize,
+ * the first 28 bytes of context->hash will contain the SHA-224 hash.
+ */
+void sha224_init(struct sha256_context *context);
+
 /*
  * Update a SHA-256 context based on the specified data.
  */

sha256test.c

@@ -57,7 +57,8 @@ int main(int argc, char **argv) {
     sha256_init(context);
     sha256_processblock(context);
     
-    printf("h[..] = %02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x "
+    
+    printf("SHA-256:%02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x "
            "%02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x\n", 
            context->hash[3], context->hash[2], context->hash[1], context->hash[0], 
            context->hash[7], context->hash[6], context->hash[5], context->hash[4], 
@@ -68,6 +69,23 @@ int main(int argc, char **argv) {
            context->hash[27], context->hash[26], context->hash[25], context->hash[24],
            context->hash[31], context->hash[30], context->hash[29], context->hash[28]);
 
+    *context = context_init;
+    
+    sha224_init(context);
+    sha256_processblock(context);
+    
+    
+    printf("SHA-224:%02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x "
+           "%02x%02x%02x%02x %02x%02x%02x%02x %02x%02x%02x%02x\n", 
+           context->hash[3], context->hash[2], context->hash[1], context->hash[0], 
+           context->hash[7], context->hash[6], context->hash[5], context->hash[4], 
+           context->hash[11], context->hash[10], context->hash[9], context->hash[8], 
+           context->hash[15], context->hash[14], context->hash[13], context->hash[12], 
+           context->hash[19], context->hash[18], context->hash[17], context->hash[16],
+           context->hash[23], context->hash[22], context->hash[21], context->hash[20],
+           context->hash[27], context->hash[26], context->hash[25], context->hash[24]);
+
+
     tick_count = GetTick();
     for (i = 0; i < 1000; i++) {
         sha256_processblock(context);