Use lookup table for faster hex encoding

Lookup table faster ~9-12 times than toString('hex') for each byte.
See https://github.com/feross/buffer/issues/219

diff --git a/index.js b/index.js
index 7c018b9c986ef9db6a368f1488d25cd8bdb8a034..9ec8a35555e5455e2d0cf0625f15ff0f4a08e1f2 100644 (file)
--- a/index.js
+++ b/index.js
@@ -1068,7 +1068,7 @@ function hexSlice (buf, start, end) {
 
   var out = ''
   for (var i = start; i < end; ++i) {
-    out += toHex(buf[i])
+    out += hexSliceNewLookupTable[buf[i]]
   }
   return out
 }
@@ -1654,11 +1654,6 @@ function base64clean (str) {
   return str
 }
 
-function toHex (n) {
-  if (n < 16) return '0' + n.toString(16)
-  return n.toString(16)
-}
-
 function utf8ToBytes (string, units) {
   units = units || Infinity
   var codePoint
@@ -1788,3 +1783,17 @@ function numberIsNaN (obj) {
   // For IE11 support
   return obj !== obj // eslint-disable-line no-self-compare
 }
+
+// Create lookup table for `toString('hex')`
+// See: https://github.com/feross/buffer/issues/219
+var hexSliceNewLookupTable = (function () {
+  var alphabet = '0123456789abcdef'
+  var table = new Array(256)
+  for (var i = 0; i < 16; ++i) {
+    var i16 = i * 16
+    for (var j = 0; j < 16; ++j) {
+      table[i16 + j] = alphabet[i] + alphabet[j]
+    }
+  }
+  return table
+})()