perf: reduce copies in jodeToDer

Brightspace · Jun 17, 2016 · a844f29 · a844f29
1 parent 7af10be
commit a844f29
Showing 1 changed file with 23 additions and 24 deletions.
diff --git a/src/ecdsa-sig-formatter.js b/src/ecdsa-sig-formatter.js
@@ -107,7 +107,7 @@ function derToJose(signature, alg) {
 	return signature;
 }
 
-function reduceBuffer(buf) {
+function countPadding(buf) {
 	var padding = 0;
 	for (var n = buf.length; padding < n && buf[padding] === 0;) {
 		++padding;
@@ -116,23 +116,9 @@ function reduceBuffer(buf) {
 	var needsSign = buf[padding] >= MAX_OCTET;
 	if (needsSign) {
 		--padding;
-
-		if (padding < 0) {
-			var old = buf;
-			buf = new Buffer(1 + buf.length);
-			buf[0] = 0;
-			old.copy(buf, 1);
-
-			return buf;
-		}
 	}
 
-	if (padding === 0) {
-		return buf;
-	}
-
-	buf = buf.slice(padding);
-	return buf;
+	return padding;
 }
 
 function joseToDer(signature, alg) {
@@ -144,10 +130,14 @@ function joseToDer(signature, alg) {
 		throw new TypeError('"' + alg + '" signatures must be "' + paramBytes * 2 + '" bytes, saw "' + signatureBytes + '"');
 	}
 
-	var r = reduceBuffer(signature.slice(0, paramBytes));
-	var s = reduceBuffer(signature.slice(paramBytes));
+	var r = signature.slice(0, paramBytes);
+	var s = signature.slice(paramBytes);
+	var rPadding = countPadding(r);
+	var sPadding = countPadding(s);
+	var rLength = r.length - rPadding;
+	var sLength = s.length - sPadding;
 
-	var rsBytes = 1 + 1 + r.length + 1 + 1 + s.length;
+	var rsBytes = 1 + 1 + rLength + 1 + 1 + sLength;
 
 	var shortLength = rsBytes < MAX_OCTET;
 
@@ -167,12 +157,21 @@ function joseToDer(signature, alg) {
 		signature[offset++] = rsBytes & 0xff;
 	}
 	signature[offset++] = ENCODED_TAG_INT;
-	signature[offset++] = r.length;
-	r.copy(signature, offset);
-	offset += r.length;
+	signature[offset++] = rLength;
+	if (rPadding < 0) {
+		signature[offset++] = 0;
+		offset += r.copy(signature, offset);
+	} else {
+		offset += r.copy(signature, offset, rPadding);
+	}
 	signature[offset++] = ENCODED_TAG_INT;
-	signature[offset++] = s.length;
-	s.copy(signature, offset);
+	signature[offset++] = sLength;
+	if (sPadding < 0) {
+		signature[offset++] = 0;
+		s.copy(signature, offset);
+	} else {
+		s.copy(signature, offset, sPadding);
+	}
 
 	return signature;
 }