buffer: add Buffer.prototype.compare by offset

Adds additional `targetStart`, `targetEnd`, `sourceStart,
and `sourceEnd` arguments to `Buffer.prototype.compare`
to allow comparison of sub-ranges of two Buffers without
requiring Buffer.prototype.slice()

Fixes: https://github.com/nodejs/node/issues/521
PR-URL: https://github.com/nodejs/node/pull/5880
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

1 files changed, 58 insertions, 0 deletions

diff --git a/benchmark/buffers/buffer-compare-offset.js b/benchmark/buffers/buffer-compare-offset.js
new file mode 100644
index 0000000000..17b36f8288
--- /dev/null
+++ b/benchmark/buffers/buffer-compare-offset.js
@@ -0,0 +1,58 @@
+'use strict';
+const common = require('../common.js');
+const v8 = require('v8');
+
+const bench = common.createBenchmark(main, {
+  method: ['offset', 'slice'],
+  size: [16, 512, 1024, 4096, 16386],
+  millions: [1]
+});
+
+function compareUsingSlice(b0, b1, len, iter) {
+
+  // Force optimization before starting the benchmark
+  Buffer.compare(b0.slice(1, len), b1.slice(1, len));
+  v8.setFlagsFromString('--allow_natives_syntax');
+  eval('%OptimizeFunctionOnNextCall(Buffer.compare)');
+  eval('%OptimizeFunctionOnNextCall(b0.slice)');
+  eval('%OptimizeFunctionOnNextCall(b1.slice)');
+  Buffer.compare(b0.slice(1, len), b1.slice(1, len));
+  doCompareUsingSlice(b0, b1, len, iter);
+}
+
+function doCompareUsingSlice(b0, b1, len, iter) {
+  var i;
+  bench.start();
+  for (i = 0; i < iter; i++)
+    Buffer.compare(b0.slice(1, len), b1.slice(1, len));
+  bench.end(iter / 1e6);
+}
+
+function compareUsingOffset(b0, b1, len, iter) {
+  len = len + 1;
+  // Force optimization before starting the benchmark
+  b0.compare(b1, 1, len, 1, len);
+  v8.setFlagsFromString('--allow_natives_syntax');
+  eval('%OptimizeFunctionOnNextCall(b0.compare)');
+  b0.compare(b1, 1, len, 1, len);
+  doCompareUsingOffset(b0, b1, len, iter);
+}
+
+function doCompareUsingOffset(b0, b1, len, iter) {
+  var i;
+  bench.start();
+  for (i = 0; i < iter; i++)
+    b0.compare(b1, 1, len, 1, len);
+  bench.end(iter / 1e6);
+}
+
+function main(conf) {
+  const iter = (conf.millions >>> 0) * 1e6;
+  const size = (conf.size >>> 0);
+  const method = conf.method === 'slice' ?
+      compareUsingSlice : compareUsingOffset;
+  method(Buffer.alloc(size, 'a'),
+         Buffer.alloc(size, 'b'),
+         size >> 1,
+         iter);
+}