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From: cline@cheetah.ece.clarkson.edu (Marshall Cline)
Newsgroups: comp.lang.c
Subject: Re: questions about a backup program for the MS-DOS environment
Message-ID: <CLINE.90May3130316@cheetah.ece.clarkson.edu>
Date: 3 May 90 17:06:11 GMT
References: <255@uecok.UUCP> <1990Apr25.125806.20450@druid.uucp>
	<12459@wpi.wpi.edu> <2484@dataio.Data-IO.COM>
Sender: news@sun.soe.clarkson.edu
Reply-To: cline@sun.soe.clarkson.edu (Marshall Cline)
Followup-To: comp.lang.c
Organization: (I don't speak for the) ECE Dept, Clarkson Univ, Potsdam, NY
Lines: 44
In-reply-to: bright@Data-IO.COM's message of 2 May 90 21:39:58 GMT

In article <2484@dataio.Data-IO.COM> bright@Data-IO.COM (Walter Bright) writes:
>In article <12459@wpi.wpi.edu> jhallen@wpi.wpi.edu (Joseph H Allen) writes:
>>In article <1990Apr25.125806.20450@druid.uucp> darcy@druid.UUCP (D'Arcy J.M. Cain) writes:
>>>In article <255@uecok.UUCP> dcrow@uecok (David Crow -- ECU Student) writes:
>>>>      - possibly a faster copying scheme.  the following is the
>>>>         code I am using to copy from one file to another:
>>>>            do
>>>>            {  n = fread(buf, sizeof(char), MAXBUF, infile);
>>>>               fwrite(buf, sizeof(char), n, outfile);
>>>>            } while (n == MAXBUF);        /* where MAXBUF = 7500 */
>>>Try:
>>>     while ((n = fread(buf, sizeof(char), BUFSIZ, infile)) != 0)
>>>		fwrite(buf, sizeof(char), n, outfile);
>>>
>>>By using BUFSIZ instead of your own buffer length you get a buffer size
>>>equal to what the fread and fwrite routines use.  
>>No, no, no Yuck!  Don't use the C functions, and don't use such tiny buffers.
>>(no wonder it's so slow :-) Try (in small or tiny model):
>>	[asm example deleted]
>There is no point in going to asm to get high speed file copies. Since it
>is inherently disk-bound, there is no sense (unless tiny code size is
>the goal). Here's a C version that you'll find is as fast as any asm code
>for files larger than a few bytes (the trick is to use large disk buffers):
[example deleted]

Note that Walter used read()/write() as opposed to fread()/fwrite().
In Turbo-C, it's even faster (probably 2 to 3 times faster!) to use
_read() and _write(), since read()/write() can end up
deleting/inserting ^J if the files are in text mode.

I found fread()/fwrite() in Turbo-C to be embarassingly & surprisingly
slow.  After tracing them, I found they resolved to loops of
fgetc()/fputc() rather than the seemingly more obvious read()/write(),
apparently since fgetc()/fputc() know about buffering.  However it
wouldn't be hard to fix fread()/fwrite() to do it `right'!

Marshall
--
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Marshall Cline/ECE Department/Clarkson University/Potsdam NY 13676/315-268-3868
 cline@sun.soe.clarkson.edu, bitnet: BH0W@CLUTX, uunet!clutx.clarkson.edu!bh0w
  Career search in progress: ECE faculty. Research oriented. Will send vita.
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