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- Path: news.connectnet.com!usenet
- From: jtara@connectnet.com (Jon Tara)
- Newsgroups: comp.graphics.algorithms,comp.lang.c++,comp.os.ms-windows.programmer.graphics,comp.os.ms-windows.programmer.multimedia,comp.os.ms-windows.programmer.win32
- Subject: Re: IJG JPEG Engine and Win32
- Date: Sat, 20 Jan 1996 16:10:33 GMT
- Organization: CONNECTnet Internet Network Services (service provider)
- Message-ID: <310110c0.44581633@news.connectnet.com>
- References: <4cemir$6vb@redstone.interpath.net> <TGL.96Jan3202549@netcom21.netcom.com> <TGL.96Jan5065424@netcom21.netcom.com> <4cpn1r$gm0@redstone.interpath.net> <4crai5$ear@hades.rz.uni-sb.de> <4d11tg$56q@redstone.interpath.net>
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- fortunat@interpath.com (Jumpstile Turner) wrote:
-
- > Incidently, malloc() and free() are measureably slower under
- >Windows 95. These generate calls to GlobalAlloc which are still in the
- >Win32 API just for compatability. Under Win32 you want to use HeapAlloc
- >or VirtualAlloc if you can.
-
- I'm not sure that using VirtualAlloc() would be such a good idea,
- except for large blocks. malloc() and free() grab large blocks and
- then divvy them up, so most of the time when you call malloc() it
- doesn't actually go out to the operating system and allocate anything.
-
- Are you sure that GlobalAlloc doesn't wind up calling
-
- >I've also been looking at sucking the JPG
- >files into RAM and decoding them from ram because JPG's tend to be
- >rather small while they're compressed. I'm not sure if I'll gain any
- >speed benefit from doing so yet.
-
- The IJG library can make use of the ability to "back up" in the file -
- that way, it can avoid allocating some buffers in some cases. Not sure
- if this really gains you much.
-
- Rather than sucking the files into RAM, though, why not just
- memory-map the file?
-
- In my app, I bring the JPG in and out through a CArchive, which
- precludes direct access to the file (I could be serializing from/to a
- CSocket, for example) and backing up. This would be a case for sucking
- it into memory first, IF there is a significant advantage to being
- able to back up.
-
- Right now, though, I'm perfectly happy with malloc() for allocation
- and letting the default MFC code (in CDocument) read the file for me.
- It seems significantly faster than Lview Pro (not sure why - I have
- the 32 bit version - is it not using the IJG code?) so I'm happy.
-
-
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