buffer: optimize decoding wrapped base64 data

The fast base64 decoder used to switch to the slow one permanently when
it saw a whitespace or other garbage character.  Since the most common
situation such characters may be encountered in is line-wrapped base64
data, a more profitable strategy is to decode a single 24-bit group with
the slow decoder and then continue running the fast algorithm.

PR-URL: https://github.com/nodejs/node/pull/12146
Ref: https://github.com/nodejs/node/issues/12114
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/benchmark/buffers/buffer-base64-decode-wrapped.js b/benchmark/buffers/buffer-base64-decode-wrapped.js
new file mode 100644
index 0000000000..aa070ab55c
--- /dev/null
+++ b/benchmark/buffers/buffer-base64-decode-wrapped.js
@@ -0,0 +1,26 @@
+'use strict';
+
+const common = require('../common.js');
+
+const bench = common.createBenchmark(main, {
+  n: [32],
+});
+
+function main(conf) {
+  const n = +conf.n;
+  const charsPerLine = 76;
+  const linesCount = 8 << 16;
+  const bytesCount = charsPerLine * linesCount / 4 * 3;
+
+  const line = 'abcd'.repeat(charsPerLine / 4) + '\n';
+  const data = line.repeat(linesCount);
+  // eslint-disable-next-line no-unescaped-regexp-dot
+  data.match(/./);  // Flatten the string
+  const buffer = Buffer.alloc(bytesCount, line, 'base64');
+
+  bench.start();
+  for (var i = 0; i < n; i++) {
+    buffer.base64Write(data, 0, bytesCount);
+  }
+  bench.end(n);
+}