Message-Id: <m0xQXwI-000S23C@inti.gov.ar>
Comments: Authenticated sender is <salvador AT natacha DOT inti DOT gov DOT ar>
From: "Salvador Eduardo Tropea (SET)" <salvador AT inti DOT edu DOT ar>
Organization: INTI
To: djgpp AT delorie DOT com
Date: Wed, 29 Oct 1997 16:19:37 +0000
MIME-Version: 1.0
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Subject: Re: malloc()
Precedence: bulk

From: "John Machin" <sjmachin AT lexicon DOT net DOT au>
Subject: malloc()
  I did a test with the Doug Lea malloc propossed by John Machin.
  I found that dlmalloc uses 2^n chunks BUT joins various of different size
to satisfy a malloc request. In this way avoids some memory wastage.
  My test was the following:

My program uses 10000 pseudo-aleatory numbers, the numbers indicates if we
will delete or allocate a block, the index in a 1024 elements array and
the size of the block (0-128Kb).

  The result was that dlmalloc wastes less memory:

BSD malloc (DJGPP) used 67305472 bytes for the heap.
dlmalloc used 51052544 bytes, that's 24% less.

  But the difference is speed is huge:

BSD malloc/free 0.22 seconds.
dlmalloc: 1.54 seconds 7 times more!!!

  I don't think is a good idea to replace the current one. Perhaps is
possible to allow the option to use dlmalloc or put it in the FAQ.
  Here is the program used (you'll need more than 64Mb free to run it ;-).

#include <stdlib.h>
#include <stdio.h>
#include <dpmi.h>
#include <go32.h>
#include <string.h>
#include <time.h>

int coreleft()
{
 _go32_dpmi_meminfo info;
 _go32_dpmi_get_free_memory_information(&info);
 return info.available_memory;
}

char *array[1024];

int main(int argc, char *argv[])
{
 char *s;
 int ori=coreleft();
 int i,index,val,del,size;
 clock_t t1,t2;

 srandom(0);
 memset(array,0,1024*4);
 t1=clock();
 for (i=0; i<10000; i++)
    {
     val=random();
     index=val & 0x3FF;
     del=val & 0x400;
     if (del)
       {
        if (array[index]!=0)
          {
           free(array[index]);
           array[index]=0;
          }
        else
           del=0;
       }
     if (!del)
       {
        size=(val>>11) & 0x1FFFF;
        if (array[index]!=0)
           free(array[index]);
        array[index]=malloc(size);
       }
    }
 t2=clock();
 printf("Memory left after it %d, used %d\n",coreleft(),ori-coreleft());
 printf("Elapsed time: %f\n",(float)(t2-t1)/CLOCKS_PER_SEC);

 return 0;
}

SET
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