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Date: Tue, 22 Oct 2002 13:52:34 -0500
From: Stephen Montgomery-Smith <stephen@math.missouri.edu>
Organization: University of Missouri
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To: Brooks Davis <brooks@one-eyed-alien.net>
Cc: Terry Lambert <tlambert2@mindspring.com>,
	Danny Braniss <danny@cs.huji.ac.il>,
	Poul-Henning Kamp <phk@critter.freebsd.dk>,
	freebsd-hackers@FreeBSD.ORG
Subject: Re: malloc
References: <E183u5Y-0003Yc-00@cse.cs.huji.ac.il> <3DB50A5A.F87EDA78@mindspring.com> <20021022110159.A1513@Odin.AC.HMC.Edu>
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Brooks Davis wrote:

 >
 > The user may also see a performance gain on Linux if they use a less
 > stupid allocation scheme.  I ran into some code once that read strings
 > one character at a time via getc() and did a realloc for each read.
 > Needless to say, performance was truly awful since a typical run
 > required parsing over 600MB of text.  I saw a better then 50% speedup on
 > Alpha Linux when I fixed that mess.
 >
 > -- Brooks
 >


As an amateur programmer, I wrote a program something like this.  But it 
allocates memory 1000 bytes at a time in order to save some of this 
overhead.  I would be interested in getting feedback about this little 
function I wrote as to whether it could be greatly improved.  (It works 
great for me, but probably I haven't really pushed it very hard.)


#include <stdio.h>
#include <stdlib.h>

/* Get a string from the stream f, allocating space to s as required.
*/

char *fgetsalloc(char **s, FILE *f) {
   int c;
   int len;
   int allocated;

   allocated = 1000;
   if ((*s = realloc(*s,1000))==NULL) {
     fprintf(stderr,"Allocation error\n");
     exit(1);
   }
   len = 0;

   while (1) {
     c=getc(f);
     if (c==EOF) break;
     if (len>=allocated-1) {
       allocated += 1000;
       if ((*s = realloc(*s,allocated))==NULL) {
         fprintf(stderr,"Allocation error\n");
         exit(1);
       }
     }
     (*s)[len] = c;
     len++;
     if (c=='\n') break;
   }
   if (len!=0) {
     (*s)[len] = '\0';
     if ((*s = realloc(*s,len+1))==NULL) {
       fprintf(stderr,"Allocation error\n");
       exit(1);
     }
   }
   else {
     if (*s!=NULL) free(*s);
     *s = NULL;
   }
   return *s;
}


-- 

Stephen Montgomery-Smith
stephen@math.missouri.edu
http://www.math.missouri.edu/~stephen


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