[Development] QStringRef conversion functions

[Keith Gardner]

Sorry to backtrack this thread, but I have some performance information.  Just FYI, I haven't made any code changes to Qt, yet.

To give some background information, I am parsing a single xml file with 88,704 floating point values using the QXmlStreamReader.  I am running in Windows 7 x64 and am using an SSD to store the file.  My compiler is Visual Studio 2010 with a Win32 configuration.

I would take the QStringRef for the argument, convert it to a string using the toString() function and then use toFloat().

	This method would parse the entire document in 608 milliseconds in release mode.
		stringRef.toString().toFloat()
	Changing that code to use wcstod on the QStringRef resulted in parsing the document in 467 millesconds.
		wcstod((const wchar_t*)stringref.unicode(),0);

In debug mode, this goes from 2814 milliseconds down to 1850 milliseconds.

I would say that there is a big payout with changing what we currently have.

Thanks,
Keith

-----Original Message-----
From: Girish Ramakrishnan [mailto:girish at forwardbias.in] 
Sent: Monday, June 11, 2012 4:55 PM
To: Keith Gardner
Cc: development at qt-project.org
Subject: Re: [Development] QStringRef conversion functions

Hi,

On Mon, Jun 11, 2012 at 11:38 AM, Keith Gardner
<kgardner at zebraimaging.com> wrote:
> I was wondering if there would be a possibility of getting some of the
> conversion functions that are in QString implemented in QStringRef (toInt,
> toFloat, etc...).  The reasoning behind this is that I am using the
> QXMLStreamReader to parse an XML file with over 88,704 floating point
> values.  I am trying to improve the speed at which the file is parsed and I
> believe one of the bottlenecks is taking an attribute of QStringRef and
> copying its data into a QString in order to convert to a float.  I would
> prefer that the copy never happen but that would require some more
> intelligence be added into the QStringRef class.
>

I am tempted to say it's 5.1 material but it would be nice to see how
much gains you are getting out of these new apis and how intrusive the
new code is. Can you push your change to gerrit ?

Thanks,
Girish