src: make base64 decoding 50% faster

Make the inner loop execute fewer compare-and-branch executions per
processed byte, resulting in a 50% or more speedup.

This coincidentally fixes an out-of-bounds read:

    while (unbase64(*src) < 0 && src < srcEnd)

Should have read:

    while (src < srcEnd && unbase64(*src) < 0)

But this commit removes the offending code altogether.

Fixes: https://github.com/nodejs/io.js/issues/2166
PR-URL: https://github.com/nodejs/io.js/pull/2193
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/benchmark/buffers/buffer-base64-decode.js b/benchmark/buffers/buffer-base64-decode.js
new file mode 100644
index 0000000000..76850c1231
--- /dev/null
+++ b/benchmark/buffers/buffer-base64-decode.js
@@ -0,0 +1,15 @@
+var assert = require('assert');
+var common = require('../common.js');
+
+var bench = common.createBenchmark(main, {});
+
+function main(conf) {
+  for (var s = 'abcd'; s.length < 32 << 20; s += s);
+  s.match(/./);  // Flatten string.
+  assert.equal(s.length % 4, 0);
+  var b = Buffer(s.length / 4 * 3);
+  b.write(s, 0, s.length, 'base64');
+  bench.start();
+  for (var i = 0; i < 32; i += 1) b.base64Write(s, 0, s.length);
+  bench.end(32);
+}