faster wcwidth with lookup table by jerch · Pull Request #798 · xtermjs/xterm.js

jerch · 2017-07-16T11:36:12Z

This PR optimizes wcwidth by using a lookup table for BMP characters. For a BMP char it boils down to a simple table lookup with some shifting magic to pack the data into 16k bytes. Speedup is at least 10 times. Equality tests included.

coveralls · 2017-07-16T11:40:13Z

Coverage decreased (-0.1%) to 70.039% when pulling b965d0a on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

coveralls · 2017-07-16T11:47:56Z

Coverage decreased (-0.1%) to 70.039% when pulling dd0fcb6 on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

coveralls · 2017-07-16T11:53:05Z

Coverage increased (+0.4%) to 70.581% when pulling 1722248 on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

coveralls · 2017-07-16T12:09:40Z

Coverage increased (+0.5%) to 70.601% when pulling 6733c6c on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

coveralls · 2017-07-16T12:13:13Z

Coverage increased (+0.5%) to 70.601% when pulling 5d87b54 on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

Tyriar

Nice ☺️

Tyriar · 2017-07-16T16:54:14Z

src/InputHandler.ts

+    }
+    return function (num) {
+        num = num | 0;
+        return (num < 65536) ? (table[num >> 2] >> ((num & 3) * 2)) & 3 : wcwidthHigh(num);


Should this have an early return for ascii characters as they are the vast majority, or would that not boost perf much at this point?

Could do with a comment explaining the bit shifting part

@Tyriar Well it gives 5% speedup to exclude the ascii range from the shifting & lookup. So yeah gonna change it.

Tyriar · 2017-07-16T16:54:59Z

src/InputHandler.ts

+        return 1;
+    }
+    let table = new Uint8Array(16384);
+    for (let i = 0; i < 16384; ++i) {


Does this increase startup in a noticeable way?

It adds 10 to 16 ms.

Is that 10-16ms when the first terminal is launched or when the script is loaded?

When the script loads, it is done during import.

Created a follow up 😃 #799

Tyriar · 2017-07-16T17:01:05Z

src/InputHandler.ts

+        }
+        return 1;
+    }
+    let table = new Uint8Array(16384);


A named variable/comment explaining 16384 would be good ((65536-4)/4+1?).

Also this needs to be conditional and fallback to a regular array for browsers without support

- commenting the bit shifts - switching to Uint32Array - conditional for TypedArray - fixing Math.floor slowdown in bisearch

coveralls · 2017-07-16T21:46:49Z

Coverage increased (+0.5%) to 70.616% when pulling 1232c00 on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

coveralls · 2017-07-16T21:57:39Z

Coverage increased (+0.4%) to 70.555% when pulling 6ed5c9e on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

jerch · 2017-07-16T22:01:34Z

@Tyriar Changed the table to Uint32Array, which speeds up the creation time (down to 6ms), it slightly slows down the reading by 20% compared to Uint8Array, dunno why. About the lazy init - I dont know where to hook it into. Is there a sumthing like a terminal-init event?

Tyriar · 2017-07-16T22:36:23Z

@jerch this would mean doing it on either terminal creation (new Terminal()) or on first request of character width (might cause async issues with the way writing works?).

… 127

jerch · 2017-07-17T17:19:53Z

Addressed the lazy loading with the last commit, the lookup table is created at the first call with a char > 127. Benchmarks with node V8 on my machine are now:

old wcwidth ASCII range (51200 times): 6.5MB in 120ms
new wcwidth ASCII range (51200 times): 6.5MB in 60ms
old wcwidth 0-65536 range (100 times): 6.5MB in 850ms
new wcwidth 0-65536 range (100 times): 6.5MB in 100ms

coveralls · 2017-07-17T17:24:11Z

Coverage increased (+0.4%) to 70.584% when pulling 598a729 on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

Tyriar

Looks good to me, I'm planning on pulling this into its own file #800 and doing a clean up so the code style is a little closer to the rest of the codebase 👍

Tyriar · 2017-07-17T18:02:49Z

src/InputHandler.test.ts

+})({nul: 0, control: 0});  // configurable options
+
+describe('wcwidth', () => {
+  it('same as old implementation for BMP and individual higher', () => {


Can't get more confident about no functional changes than this 😉

coveralls · 2017-07-17T18:29:26Z

Coverage increased (+0.4%) to 70.564% when pulling 20048d3 on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

Tyriar · 2017-07-17T20:08:53Z

@jerch CI failed on macOS:

  181 passing (5s)
  1 failing
  1) wcwidth same as old implementation for BMP and individual higher:
     Error: Timeout of 2000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves.

Might need to increase the timeout of that test? https://travis-ci.org/sourcelair/xterm.js/jobs/254546569

jerch · 2017-07-17T21:22:40Z

Hmm yeah seems the travis OSX boxes are pretty busy from time to time and tend timeout longer running tests. The test runs in under a second here...

coveralls · 2017-07-18T20:58:41Z

Coverage increased (+0.4%) to 70.589% when pulling cd5827e on jerch:faster_wcwidth into 48dab49 on sourcelair:master.

faster wcwidth with lookup table

b965d0a

jerch mentioned this pull request Jul 16, 2017

Buffer performance improvements #791

Closed

fixing whitespaces

dd0fcb6

fixing whitespaces

1722248

jerch added 3 commits July 16, 2017 13:57

fixing whitespaces

ba2d0e8

test speedup defensive

6733c6c

test speedup defensive

5d87b54

Tyriar requested changes Jul 16, 2017

View reviewed changes

some fixes

1232c00

- commenting the bit shifts - switching to Uint32Array - conditional for TypedArray - fixing Math.floor slowdown in bisearch

speed test commented out

6ed5c9e

fixes #799 - lookup table is created on first wcwidth call for char >…

598a729

… 127

Tyriar mentioned this pull request Jul 17, 2017

Pull wcwidth into its own file #800

Closed

Tyriar approved these changes Jul 17, 2017

View reviewed changes

Tyriar added this to the 2.9.0 milestone Jul 17, 2017

Merge branch 'master' into faster_wcwidth

20048d3

higher timeout for test case

cd5827e

Tyriar merged commit 05d308a into xtermjs:master Jul 18, 2017

jerch mentioned this pull request Nov 14, 2018

initTable is slow, can we lazily load parts as they're needed? #1785

Closed

jerch mentioned this pull request May 20, 2023

working perf test and API test injection PerBothner/xterm.js#2

Merged

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