add function for one-off calculation (#45)

hash/sha3/sha3.go

@@ -132,14 +132,10 @@ func (c *state) Write(in []byte) (nwrite int, err error) {
 	return nwrite, nil
 }
 
-// Read changes state of the hash if called first time. It will
-// return len(out) bytes of data. Never fails.
-func (c *state) Read(out []byte) (nread int, err error) {
+func (c *state) finalize_sha3() {
 	buf := c.data.asBytes()[:]
 	rate := c.BlockSize()
-	nread = len(out)
 
-	if !c.isSquezing {
 	// there is at least one byte free, otherise
 	// buf would be squezed already
 	for i := c.idx + 1; i < rate; i++ {
@@ -152,6 +148,17 @@ func (c *state) Read(out []byte) (nread int, err error) {
 	copyOut(c, buf[:rate])
 	c.idx = rate // now, idx indicates unconsumed amount of data
 	c.isSquezing = true
+}
+
+// Read changes state of the hash if called first time. It will
+// return len(out) bytes of data. Never fails.
+func (c *state) Read(out []byte) (nread int, err error) {
+	buf := c.data.asBytes()[:]
+	rate := c.BlockSize()
+	nread = len(out)
+
+	if !c.isSquezing {
+		c.finalize_sha3()
 	}
 
 	// Copy-out bytes that are still kept in the buffer
@@ -211,6 +218,21 @@ func (c *state) Sum(in []byte) []byte {
 	return in
 }
 
+func (c *state) digest(out, in []byte) {
+	nread := len(out)
+	rate := c.BlockSize()
+	nblocks := nread / rate
+	c.Write(in)
+	c.finalize_sha3()
+	for i := 0; i < nblocks-1; i++ {
+		keccakF1600(&c.a)
+		copyOut(c, out[:])
+		out = out[rate:]
+	}
+	keccakF1600(&c.a)
+	copyOut(c, out[:len(out)])
+}
+
 // New224 creates a new SHA3-224 hash.
 // Its generic security strength is 224 bits against preimage attacks,
 // and 112 bits against collision attacks.