1294616 - Somewhat improve the string performance over bug 1288320

Status: RESOLVED FIXED

(Core :: Audio/Video: Playback, defect, P3)

Description

[JW Wang [:jwwang] [:jw_wang]]

By defining
static constexpr auto& str = "hello";
instead of
static const char* const str = "hello";

The length is known at compile time and we can call EqualsLiteral() instead of EqualsASCII() to slightly improve the performance.

Comment 1

[JW Wang [:jwwang] [:jw_wang]]

Attachment: Bug 1294616 - Somewhat improve the string performance by defining string literals whose length is known at compile time.

Review commit: https://reviewboard.mozilla.org/r/71472/diff/#index_header
See other reviews: https://reviewboard.mozilla.org/r/71472/

Comment 2

[JW Wang [:jwwang] [:jw_wang]]

Comment on attachment 8780964 [details]
Bug 1294616 - Somewhat improve the string performance by defining string literals whose length is known at compile time.

Review request updated; see interdiff: https://reviewboard.mozilla.org/r/71472/diff/1-2/

Comment 3

[Chris Pearce [:cpearce (Not reading bugmail)]]

Comment on attachment 8780964 [details]
Bug 1294616 - Somewhat improve the string performance by defining string literals whose length is known at compile time.

https://reviewboard.mozilla.org/r/71472/#review71568

::: dom/media/eme/EMEUtils.cpp:138
(Diff revision 2)
>  }
>  
>  nsString
>  KeySystemToGMPName(const nsAString& aKeySystem)
>  {
> -  if (aKeySystem.EqualsASCII(kEMEKeySystemPrimetime)) {
> +  if (aKeySystem.EqualsASCII(kEMEKeySystemPrimetime.get(),

I'm not super keen on having to manually pass the length and raw char pointer to this. Can you use CompareUTF8toUTF16() instead? That does a length check too.

Comment 4

[JW Wang [:jwwang] [:jw_wang]]

Sure. Thanks for the review!

Comment 5

[Chris Pearce [:cpearce (Not reading bugmail)]]

Though, I would have thought you could use nsAString::EqualsLiteral(const char*) instead to get what you wanted?

Comment 6

[JW Wang [:jwwang] [:jw_wang]]

nsAString::EqualsLiteral is less efficient for it doesn't have the length.

Comment 7

[JW Wang [:jwwang] [:jw_wang]]

We have 3 strings to compare:
org.w3.clearkey
com.widevine.alpha
com.adobe.primetime

with different lengths.

So the compare functions can run in constant time when length is given.

Comment 8

[JW Wang [:jwwang] [:jw_wang]]

Comment on attachment 8780964 [details]
Bug 1294616 - Somewhat improve the string performance by defining string literals whose length is known at compile time.

Review request updated; see interdiff: https://reviewboard.mozilla.org/r/71472/diff/2-3/

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3d01226b50ef
Somewhat improve the string performance by defining string literals whose length is known at compile time. r=cpearce

Comment 10

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/3d01226b50ef