feat: improve performance of v1 string representation (#453)

Pre-allocate a fixed size array instead of an empty array when no array is passed.

examples/benchmark/benchmark.js

@@ -21,7 +21,13 @@ suite
     uuidv1();
   })
   .add('uuidv1() fill existing array', function () {
-    uuidv1(null, array, 0);
+    try {
+      uuidv1(null, array, 0);
+    } catch (err) {
+      // The spec (https://tools.ietf.org/html/rfc4122#section-4.2.1.2) defines that only 10M/s v1
+      // UUIDs can be generated on a single node. This library throws an error if we hit that limit
+      // (which can happen on modern hardware and modern Node.js versions).
+    }
   })
   .add('uuidv4()', function () {
     uuidv4();

src/bytesToUuid.js

@@ -8,34 +8,30 @@ for (let i = 0; i < 256; ++i) {
   byteToHex.push((i + 0x100).toString(16).substr(1));
 }
 
-function bytesToUuid(buf, offset) {
-  const i = offset || 0;
-
-  const bth = byteToHex;
-
+function bytesToUuid(buf, offset = 0) {
   // Note: Be careful editing this code!  It's been tuned for performance
   // and works in ways you may not expect. See https://github.com/uuidjs/uuid/pull/434
   return (
-    bth[buf[i + 0]] +
-    bth[buf[i + 1]] +
-    bth[buf[i + 2]] +
-    bth[buf[i + 3]] +
+    byteToHex[buf[offset + 0]] +
+    byteToHex[buf[offset + 1]] +
+    byteToHex[buf[offset + 2]] +
+    byteToHex[buf[offset + 3]] +
     '-' +
-    bth[buf[i + 4]] +
-    bth[buf[i + 5]] +
+    byteToHex[buf[offset + 4]] +
+    byteToHex[buf[offset + 5]] +
     '-' +
-    bth[buf[i + 6]] +
-    bth[buf[i + 7]] +
+    byteToHex[buf[offset + 6]] +
+    byteToHex[buf[offset + 7]] +
     '-' +
-    bth[buf[i + 8]] +
-    bth[buf[i + 9]] +
+    byteToHex[buf[offset + 8]] +
+    byteToHex[buf[offset + 9]] +
     '-' +
-    bth[buf[i + 10]] +
-    bth[buf[i + 11]] +
-    bth[buf[i + 12]] +
-    bth[buf[i + 13]] +
-    bth[buf[i + 14]] +
-    bth[buf[i + 15]]
+    byteToHex[buf[offset + 10]] +
+    byteToHex[buf[offset + 11]] +
+    byteToHex[buf[offset + 12]] +
+    byteToHex[buf[offset + 13]] +
+    byteToHex[buf[offset + 14]] +
+    byteToHex[buf[offset + 15]]
   ).toLowerCase();
 }
 

src/v1.js

@@ -16,7 +16,7 @@ let _lastNSecs = 0;
 // See https://github.com/uuidjs/uuid for API details
 function v1(options, buf, offset) {
   let i = (buf && offset) || 0;
-  const b = buf || [];
+  const b = buf || new Array(16);
 
   options = options || {};
   let node = options.node || _nodeId;
@@ -27,6 +27,7 @@ function v1(options, buf, offset) {
   // system entropy.  See #189
   if (node == null || clockseq == null) {
     const seedBytes = options.random || (options.rng || rng)();
+
     if (node == null) {
       // Per 4.5, create and 48-bit node id, (47 random bits + multicast bit = 1)
       node = _nodeId = [
@@ -38,6 +39,7 @@ function v1(options, buf, offset) {
         seedBytes[5],
       ];
     }
+
     if (clockseq == null) {
       // Per 4.2.2, randomize (14 bit) clockseq
       clockseq = _clockseq = ((seedBytes[6] << 8) | seedBytes[7]) & 0x3fff;