Update hexSlice to use TypedArrays and TextDecoder for large speed gains

.gitignore

@@ -2,3 +2,5 @@
 .airtap.yml
 *.log
 node_modules/
+package-lock.json
+perf/bundle.js

AUTHORS.md

@@ -69,6 +69,13 @@
 - jkkang (jkkang@smartauth.kr)
 - Deklan Webster (deklanw@gmail.com)
 - Martin Heidegger (martin.heidegger@gmail.com)
-- junderw (junderwood@bitcoinbank.co.jp)
+- André Werlang (589286+awerlang@users.noreply.github.com)
+- Bradley Odell (btodell@hotmail.com)
+- Dominik Moritz (domoritz@gmail.com)
+- Rachel Simone Weil (partytimehexcellent@gmail.com)
+- Patrick McAndrew (urg@users.noreply.github.com)
+- Jonathan Underwood (jonathan.underwood4649@gmail.com)
+- Christopher Jeffrey (JJ) (chjjeffrey@gmail.com)
+- George MacKerron (george@mackerron.co.uk)
 
 #### Generated by bin/update-authors.sh.

index.js

@@ -1083,16 +1083,45 @@ function latin1Slice (buf, start, end) {
 }
 
 function hexSlice (buf, start, end) {
-  const len = buf.length
+  const buflen = buf.length
 
   if (!start || start < 0) start = 0
-  if (!end || end < 0 || end > len) end = len
+  if (!end || end < 0 || end > buflen) end = buflen
 
-  let out = ''
-  for (let i = start; i < end; ++i) {
-    out += hexSliceLookupTable[buf[i]]
+  buf = buf.subarray(start, end)  // `slice` is deprecated
+
+  // buffer needs to be 4-byte aligned for what follows
+  if (buf.byteOffset % 4 !== 0) buf = new Uint8Array(buf)
+
+  const len = buf.length
+  const halfLen = len >>> 1
+  const quarterLen = len >>> 2
+  const out16 = new Uint16Array(len)
+  const buf32 = new Uint32Array(buf.buffer, buf.byteOffset, quarterLen)
+  const out32 = new Uint32Array(out16.buffer, out16.byteOffset, halfLen)
+  const lt = hexSliceLookupTable
+
+  // read 4 bytes (1x uint32) and write 8 bytes (2x uint32) at a time
+  let i = 0
+  let j = 0
+  let v
+  if (littleEndian) while (i < quarterLen) {
+    v = buf32[i++]
+    out32[j++] = lt[(v >>> 8) & 255] << 16 | lt[v & 255]
+    out32[j++] = lt[v >>> 24] << 16 | lt[(v >>> 16) & 255]
   }
-  return out
+  else while (i < quarterLen) {
+    v = buf32[i++]
+    out32[j++] = lt[v >>> 24] << 16 | lt[(v >>> 16) & 255]
+    out32[j++] = lt[(v >>> 8) & 255] << 16 | lt[v & 255]
+  }
+
+  // deal with up to 3 remaining bytes
+  i <<= 2;  // uint32 addressing to uint8 addressing
+  while (i < len) out16[i] = lt[buf[i++]]
+
+  const hex = textDecoder.decode(out16.subarray(0, len))
+  return hex
 }
 
 function utf16leSlice (buf, start, end) {
@@ -2091,16 +2120,17 @@ function numberIsNaN (obj) {
   return obj !== obj // eslint-disable-line no-self-compare
 }
 
-// Create lookup table for `toString('hex')`
-// See: https://github.com/feross/buffer/issues/219
+// Create lookup table etc. for `toString('hex')`
+const textDecoder = new TextDecoder()
+const littleEndian = new Uint8Array((new Uint16Array([0x0102]).buffer))[0] === 0x02
 const hexSliceLookupTable = (function () {
-  const alphabet = '0123456789abcdef'
-  const table = new Array(256)
-  for (let i = 0; i < 16; ++i) {
-    const i16 = i * 16
-    for (let j = 0; j < 16; ++j) {
-      table[i16 + j] = alphabet[i] + alphabet[j]
-    }
+  const alphabet = new TextEncoder().encode('0123456789abcdef')
+  const table = new Uint16Array(256)
+  if (littleEndian) for (let i = 0; i < 256; i++) {
+    table[i] = alphabet[i & 0xF] << 8 | alphabet[i >>> 4]
+  }
+  else for (let i = 0; i < 256; i++) {
+    table[i] = alphabet[i & 0xF] | alphabet[i >>> 4] << 8
   }
   return table
 })()

package.json

@@ -59,7 +59,7 @@
   },
   "scripts": {
     "perf": "browserify --debug perf/bracket-notation.js > perf/bundle.js && open perf/index.html",
-    "perf-node": "node perf/bracket-notation.js && node perf/concat.js && node perf/copy-big.js && node perf/copy.js && node perf/new-big.js && node perf/new.js && node perf/readDoubleBE.js && node perf/readFloatBE.js && node perf/readUInt32LE.js && node perf/slice.js && node perf/writeFloatBE.js && node perf/write-hex.js",
+    "perf-node": "node perf/bracket-notation.js && node perf/concat.js && node perf/copy-big.js && node perf/copy.js && node perf/new-big.js && node perf/new.js && node perf/readDoubleBE.js && node perf/readFloatBE.js && node perf/readUInt32LE.js && node perf/slice.js && node perf/toString-hex.js && node perf/writeFloatBE.js && node perf/write-hex.js",
     "size": "browserify -r ./ | uglifyjs -c -m | gzip | wc -c",
     "standard": "standard",
     "test": "tape test/*.js test/node/*.js",

perf/toString-hex.js

@@ -0,0 +1,21 @@
+const BrowserBuffer = require('../').Buffer // (this module)
+const util = require('./util')
+const suite = util.suite()
+
+const LENGTH = 4096
+const browserSubject = BrowserBuffer.alloc(LENGTH)
+const nodeSubject = Buffer.alloc(LENGTH)
+
+for (let i = 0; i < LENGTH; i++) {
+  browserSubject[i] = nodeSubject[i] = (Math.random() * 255) << 0
+}
+
+suite
+  .add('BrowserBuffer#toString("hex")', function () {
+    browserSubject.toString('hex')
+  })
+
+if (!process.browser) suite
+  .add('NodeBuffer#toString("hex")', function () {
+    nodeSubject.toString('hex')
+  })