lib: add ASCII fast path to getStringWidth()

A lot of strings that are going to be passed to `getStringWidth()`
are ASCII strings, for which the calculation is rather easy and
calling into C++ can be skipped.

                                                       confidence improvement accuracy (*)    (**)   (***)
     misc/getstringwidth.js n=100000 type='ascii'            ***    328.99 %      ±21.73% ±29.25% ±38.77%
     misc/getstringwidth.js n=100000 type='emojiseq'                  2.94 %       ±7.66% ±10.19% ±13.26%
     misc/getstringwidth.js n=100000 type='fullwidth'                 4.70 %       ±5.64%  ±7.50%  ±9.76%

PR-URL: https://github.com/nodejs/node/pull/29301
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

1 files changed, 26 insertions, 0 deletions

diff --git a/benchmark/misc/getstringwidth.js b/benchmark/misc/getstringwidth.js
new file mode 100644
index 0000000000..12f071c60d
--- /dev/null
+++ b/benchmark/misc/getstringwidth.js
@@ -0,0 +1,26 @@
+'use strict';
+
+const common = require('../common.js');
+
+const bench = common.createBenchmark(main, {
+  type: ['ascii', 'mixed', 'emojiseq', 'fullwidth'],
+  n: [10e4]
+}, {
+  flags: ['--expose-internals']
+});
+
+function main({ n, type }) {
+  const { getStringWidth } = require('internal/readline/utils');
+
+  const str = ({
+    ascii: 'foobar'.repeat(100),
+    mixed: 'foo'.repeat(100) + '😀' + 'bar'.repeat(100),
+    emojiseq: '👨‍👨‍👧‍👦👨‍👩‍👦‍👦👨‍👩‍👧‍👧👩‍👩‍👧‍👦'.repeat(10),
+    fullwidth: '你好'.repeat(150)
+  })[type];
+
+  bench.start();
+  for (let j = 0; j < n; j += 1)
+    getStringWidth(str);
+  bench.end(n);
+}