Language/OS - Multiplatform Resource Library/LANGUAGE OS.iso/oper_sys/presto/prest_04.lha/src/shmalloc.c

C/C++ Source or Header | 1989-08-08 | 22.5 KB | 862 lines

/*
 * This memory allocation code is derived from the GNU memory allocator.
 * Please read the FSF copyright notice at the end of this file.
 */

/*
 * @(#)nmalloc.c 1 (Caltech) 2/21/82
 *
 *    U of M Modified: 20 Jun 1983 ACT: strange hacks for Emacs
 *
 *    Nov 1983, Mike@BRL, Added support for 4.1C/4.2 BSD.
 *
 * This is a very fast storage allocator.  It allocates blocks of a small
 * number of different sizes, and keeps free lists of each size.  Blocks
 * that don't exactly fit are passed up to the next larger size.  In this
 * implementation, the available sizes are (2^n)-4 (or -16) bytes long.
 * This is designed for use in a program that uses vast quantities of
 * memory, but bombs when it runs out.  To make it a little better, it
 * warns the user when he starts to get near the end.
 *
 * June 84, ACT: modified rcheck code to check the range given to malloc,
 * rather than the range determined by the 2-power used.
 *
 * Jan 85, RMS: calls malloc_warning to issue warning on nearly full.
 * No longer Emacs-specific; can serve as all-purpose malloc for GNU.
 * You should call malloc_init to reinitialize after loading dumped Emacs.
 * Call malloc_stats to get info on memory stats if MSTATS turned on.
 * realloc knows how to return same block given, just changing its size,
 * if the power of 2 is correct.
 *
 * May 88, Univ. of Washington: Significant (but relatively simple)
 * changes to make this code work in a Sequent shared-memory/PRESTO
 * environment.
 *
 * Perhaps the biggest difference is that whenever we have to ask for
 * more space, we get a BIG chunk rather than a relatively small one.
 * Another change is that requests for memory >= the system page size
 * will return memory that is aligned to a page boundary, due to the
 * prevalent use of mmap(2).
 *
 * June 89, Univ. of Washington: Worked on memory alignment bug in malloc().
 *
 * Most of the changes are bracketed by the SHARED and PRESTO $ifdef's.
 *
 */


#define SHARED
#define PRESTO

#include <sys/types.h>

#ifdef SHARED

#ifdef sequent
#include <parallel/parallel.h>
#define sbrk shsbrk
#endif sequent

#ifdef sun
#  define shared /**/
#  define private /**/
   typedef    int slock_t;
#  define L_UNLOCKED 0
#  ifdef PRESTO
#      define S_LOCK s_lock
#      define S_UNLOCK s_unlock
#  endif PRESTO
#endif sun

#ifdef vax
#define shared /**/
#define private /**/
typedef    int slock_t;
#define L_UNLOCKED 0

#ifdef PRESTO
/*
 * Redefine S_LOCK and S_UNLOCK to be s_lock() and s_unlock(),
 * included in vax_lock.s in Presto source.  Should probably be
 * asm macros.  On the vax, the shared allocation code won't ld
 * outside of a presto environment.
 */
#define S_LOCK s_lock
#define S_UNLOCK s_unlock
#else
XXX
#endif PRESTO
#endif vax

#ifdef PRESTO
/*
 * See comment on naming of the memory allocator in misc.c.
 *
 * #define malloc shmalloc
 * #define free shfree
 */

#endif PRESTO

#define mstats shmstats
#define realloc shrealloc

#endif SHARED

#ifdef PRESTO
/*
 * These external routines are needed to avoid a deadlock situation where
 * we preempt a thread controlling access to the memory management
 * stuff.  Preempting while holding onto this stuff could make things
 * go very very slowly.
 */

extern void enable_interrupts();
extern int disable_interrupts();
#endif PRESTO


/*
 * Determine which kind of system this is.
 */
#define BSD42
#define BSD
#include <sys/time.h>
#include <sys/resource.h>

#define ISALLOC ((char) 0xf7)    /* magic byte that implies allocation */
#define ISFREE ((char) 0x54)    /* magic byte that implies free block */
                /* this is for error checking only */
#define ISMEMALIGN ((char) 0xd6)  /* Stored before the value returned by
                     memalign, with the rest of the word
                     being the distance to the true
                     beginning of the block.  */

/*
 * NBINS == number of "headers" pointing to blocks of size 2**(n+3).
 */
#define NBINS 30

/*
 * If MSTATS is defined then
 * nmalloc[i] is the difference between the number of mallocs and frees
 * for a given block size.
 */

#ifdef MSTATS
#ifdef SHARED
shared static int nmalloc[NBINS];
shared static int nmal, nfre;
#else
static int nmalloc[NBINS];
static int nmal, nfre;
#endif
#endif /* MSTATS */

/*
 * If range checking is not turned on, all we have is a flag indicating
 * whether memory is allocated, an index in nextf[], and a size field; to
 * realloc() memory we copy either size bytes or 1<<(index+3) bytes depending
 * on whether the former can hold the exact size (given the value of
 * 'index').  If range checking is on, we always need to know how much space
 * is allocated, so the 'size' field is only used to remember memory alignment
 */

struct mhead {
    char     mh_alloc;    /* ISALLOC or ISFREE */
    char     mh_index;    /* index in nextf[] */
/* Remainder are valid only when block is allocated */
    unsigned short mh_size;    /* size, if < 0x10000 */
#ifdef rcheck
    unsigned mh_nbytes;    /* number of bytes allocated */
    int      mh_magic4;    /* should be == MAGIC4 */
#endif /* rcheck */
};

/*
 * Access free-list pointer of a block.
 * It is stored at block + 4.
 * This is not a field in the mhead structure
 * because we want sizeof (struct mhead)
 * to describe the overhead for when the block is in use,
 * and we do not want the free-list pointer to count in that.
 */

#define CHAIN(a) \
  (*(struct mhead **) (sizeof (char *) + (char *) (a)))

#ifdef rcheck

/*
 * To implement range checking, we write magic values in at the beginning and
 * end of each allocated block, and make sure they are undisturbed whenever a
 * free or a realloc occurs.
 */

/* Written in each of the 4 bytes following the block's real space */
#define MAGIC1 0x55

/* Written in the 4 bytes before the block's real space */
#define MAGIC4 0x55555555

#define ASSERT(p) if (!(p)) botch("p"); else
#define EXTRA  4        /* 4 bytes extra for MAGIC1s */

#else

#define ASSERT(p)
#define EXTRA  0

#endif /* rcheck */

/*
 * nextf[i] is the pointer to the next free block of size 2^(i+3).  The
 * smallest allocatable block is 8 bytes.  The overhead information will
 * go in the first int of the block, and the returned pointer will point
 * to the second.
 *
 * busy[i] is meant to indicate that a recursive call to malloc
 * has been made (e.g., via a signal handler). Not used in this
 * (May 88) version.
 */

#ifdef SHARED
/* nextf[i] is free list of blocks of size 2**(i + 3)  */
shared static struct mhead *nextf[NBINS];

/* busy[i] is nonzero while allocation of block size i is in progress.  */
shared static char busy[NBINS];

/* Number of bytes of writable memory we can expect to be able to get */
shared static unsigned int lim_data;

/* nonzero once initial bunch of free blocks made */
shared static int gotpool;

/* Mutex for structure access */
shared static slock_t lock;

/* System page size in bytes */
shared static int syspgsize;

#ifdef PRESTO

#define BEGIN_CRITICAL {        \
    disable_interrupts();        \
    S_LOCK(&lock);            \
}

#define END_CRITICAL {            \
    S_UNLOCK(&lock);        \
    enable_interrupts();        \
}

#else

#define BEGIN_CRITICAL {        \
    S_LOCK(&lock);            \
}

#define END_CRITICAL {            \
    S_UNLOCK(&lock);        \
}

#endif PRESTO

#else    /* not shared */

#ifdef PRESTO

#define BEGIN_CRITICAL disable_interrupts();
#define END_CRITICAL enable_interrupts();

#else

#define BEGIN_CRITICAL ;
#define END_CRITICAL ;

#endif PRESTO

/* nextf[i] is free list of blocks of size 2**(i + 3)  */
static struct mhead *nextf[NBINS];

/* busy[i] is nonzero while allocation of block size i is in progress.  */
static char busy[NBINS];

/* Number of bytes of writable memory we can expect to be able to get */
static unsigned int lim_data;

/* nonzero once initial bunch of free blocks made */
static int gotpool;

/* System page size in bytes */
static int syspgsize;

#endif SHARED

char *grab_hunk();

/*
 * BRKSIZELOG2 is log2-3 of the minimum chunk of memory we will ask for
 * if we have to request more memory (ie, via sbrk).  In our case we ask for
 * the maximum that will fit in the mh_size field, 65K.
 */
#define BRKSIZELOG2 13

static morecore (nu)            /* ask system for more memory */
    register int nu;        /* size index to get more of  */
{
    register char *cp;
    register int nblks;
    register unsigned int siz;

 /*
  * On initial startup, get one block of each size up to some reasonable
  * size.
  */
  if (!gotpool) {
    getpool ();
    gotpool = 1;
    if ( nextf[nu] ) return; /* Getpool got it for us */
   }

 /*
  * Must be either a big block or we are really out of memory.
  */
  nblks = 1;
  if ((siz = nu) < BRKSIZELOG2)
    nblks = 1 << ((siz = BRKSIZELOG2) - nu);

  if ((cp = grab_hunk(1 << (siz + 3))) == (char *) -1)
    return;            /* no more room! */

  if ((int) cp & 7) {
    /*
     * shouldn't happen, but just in case
     */
    cp = (char *) (((int) cp + 8) & ~7);
    nblks--;
  }

  /*
   * save new header and link the nblks blocks together
   */
  nextf[nu] = (struct mhead  *) cp;
  siz = 1 << (nu + 3);
  while (1) {
    ((struct mhead *) cp) -> mh_alloc = ISFREE;
    ((struct mhead *) cp) -> mh_index = nu;
    if (--nblks <= 0)
    break;
    CHAIN ((struct mhead   *) cp) = (struct mhead  *) (cp + siz);
    cp += siz;
  }
  CHAIN ((struct mhead   *) cp) = 0;
}

/*
 * Get a chunk of memory from the system.  Make sure the pointer that
 * we return is just sizeof(struct mhead) bytes shy of a page boundary.
 * Calls to this function must be serialized.
 */

char *
grab_hunk(nbytes)
  int nbytes;
{
  char *cp;
  char *sbrk ();

  cp = sbrk(0);
  /*
   * land on pagesize boundaries
   */
  if (((int) cp + sizeof(struct mhead)) & (syspgsize-1)) {
    sbrk (syspgsize - (((int) cp + sizeof( struct mhead)) & (syspgsize-1)));
  }

  return(sbrk(nbytes));
}

/*
 * Get a chunk of memory from the system.  Make sure the pointer that
 * we return is just on a page boundary.  This memory should **not**
 * be used by the memory allocator.
 */

char *
grab_nonmalloc_hunk(nbytes)
  int nbytes;
{
  char *cp;
  char *sbrk ();

  BEGIN_CRITICAL;
  cp = sbrk(0);
  /*
   * land on pagesize boundaries
   */
  if (((int) cp) & (syspgsize-1)) {
    sbrk (syspgsize - (((int) cp) & (syspgsize-1)));
  }

  cp = sbrk(nbytes);
  END_CRITICAL;
  return cp;
}

static getpool ()
{
  register int nu;
  register char *cp;
  int logpgsz;

  /* Get 16*pagesize of storage */
  cp = grab_hunk(16*syspgsize);
  if (cp == (char *) -1)
    return;

  /*
  /* Divide it into an initial 8-word block
   * plus one block of size 2**nu for nu = 3 ... log2(chunksize*pgsize)-1.
   */
  logpgsz = 8*syspgsize;
  nu = 0;
  while ( ! (logpgsz & 1) ) {
      logpgsz >>= 1;
      nu++;
  }
  logpgsz = nu - 3;

  CHAIN (cp) = nextf[0];
  nextf[0] = (struct mhead *) cp;
  ((struct mhead *) cp) -> mh_alloc = ISFREE;
  ((struct mhead *) cp) -> mh_index = 0;
  cp += 8;

  for (nu = 0; nu < logpgsz; nu++)
    {
      CHAIN (cp) = nextf[nu];
      nextf[nu] = (struct mhead *) cp;
      ((struct mhead *) cp) -> mh_alloc = ISFREE;
      ((struct mhead *) cp) -> mh_index = nu;
      cp += 8 << nu;
    }
}

char *malloc (n)        /* get a block */
     unsigned n;
{
  register struct mhead *p;
  register unsigned int nbytes;
  register int nunits = 0;
  int mustalign;
  char *aligned;
  struct mhead *p2;

  /*
   * Figure out how many bytes are required, rounding up to the nearest
   * multiple of 4, then figure out which nextf[] area to use.
   */
  if ( !syspgsize ) {
      syspgsize = getpagesize();
  }

  /*
   * If asking for >= syspgsize bytes, make sure
   * the return value is page aligned in case of mmap(2).
   */
  if ( n >= syspgsize ) {
    mustalign = 1;
      n += syspgsize;
  }
  else {
    mustalign = 0;
  }

  nbytes = (n + sizeof *p + EXTRA + 3) & ~3;
  {
    register unsigned int   shiftr = (nbytes - 1) >> 2;

    while (shiftr >>= 1)
      nunits++;
  }

  BEGIN_CRITICAL;

  /* If there are no blocks of the appropriate size, go get some */
  /* COULD SPLIT UP A LARGER BLOCK HERE ... ACT */
  if (nextf[nunits] == 0)
    morecore (nunits);

  /* Get one block off the list, and set the new list head */
  if ((p = nextf[nunits]) == 0) {
      END_CRITICAL;
      return 0;
  }

  nextf[nunits] = CHAIN (p);

  END_CRITICAL;

  /*
   * Check for free block clobbered
   * If not for this check, we would gobble a clobbered free chain ptr
   * and bomb out on the NEXT allocate of this size block
   */
  if (p -> mh_alloc != ISFREE || p -> mh_index != nunits)
#ifdef rcheck
    botch ("block on free list clobbered");
#else /* not rcheck */
    abort ();
#endif /* not rcheck */

  /* Fill in the info, and if range checking, set up the magic numbers */
  p -> mh_alloc = ISALLOC;

#ifdef rcheck
  p -> mh_nbytes = n;
  p -> mh_magic4 = MAGIC4;
  {
    register char  *m = (char *) (p + 1) + n;

    *m++ = MAGIC1, *m++ = MAGIC1, *m++ = MAGIC1, *m = MAGIC1;
  }
#else /* not rcheck */
  p -> mh_size = n;
#endif /* not rcheck */

#ifdef MSTATS
  nmalloc[nunits]++;
  nmal++;
#endif /* MSTATS */

  if ( mustalign ) {
      if ( ((int)(p+1) & (syspgsize-1)) != 0 ) {
      aligned = (char *) (p+1);
      aligned = (char *) (((int)aligned + syspgsize - 1) & -syspgsize);
      p2 = (struct mhead *) aligned - 1;
      p2->mh_size = aligned - (char *)( p + 1 );
      p2->mh_alloc = ISMEMALIGN;
      return aligned;
      }
  }

  return (char *) (p + 1);
}

free (mem)
     char *mem;
{
  register struct mhead *p;

  {
    register char *ap = mem;

    if (ap == 0)
      return;

    p = (struct mhead *) ap - 1;
    if (p -> mh_alloc == ISMEMALIGN)
      {
    ap -= p->mh_size;
    p = (struct mhead *) ap - 1;
      }

    if (p -> mh_alloc != ISALLOC)
#ifdef rcheck
      abort ();
#else
      return;
#endif
#ifdef rcheck
    ASSERT (p -> mh_magic4 == MAGIC4);
    ap += p -> mh_nbytes;
    ASSERT (*ap++ == MAGIC1); ASSERT (*ap++ == MAGIC1);
    ASSERT (*ap++ == MAGIC1); ASSERT (*ap   == MAGIC1);
#endif /* rcheck */

  }

  {
    register int nunits = p -> mh_index;

    ASSERT (nunits <= (NBINS-1));
    p -> mh_alloc = ISFREE;

    BEGIN_CRITICAL;

    /* Put this block on the free list.  */
    CHAIN (p) = nextf[nunits];
    nextf[nunits] = p;

#ifdef MSTATS
    nmalloc[nunits]--;
    nfre++;
#endif /* MSTATS */

    END_CRITICAL;
  }
}


#ifdef MSTATS
/*
 * Return statistics describing allocation of blocks of size 2**n.
 *
 * This seems like a foolish way to do things, but who am I to argue
 * with Stallman, et al.
 */

struct mstats_value {
    int blocksize;
    int nfree;
    int nused;
};

struct mstats_value malloc_stats (size)
     int size;
{
  struct mstats_value v;
  register int i;
  register struct mhead *p;

  v.nfree = 0;

  if (size < 0 || size >= NBINS)
    {
      v.blocksize = 0;
      v.nused = 0;
      return v;
    }

  BEGIN_CRITICAL;
  v.blocksize = 1 << (size + 3);
  v.nused = nmalloc[size];
  for (p = nextf[size]; p; p = CHAIN (p))
    v.nfree++;
  END_CRITICAL;

  return v;
}
#endif /* MSTATS */

char *realloc (mem, n)
    char *mem;
    register unsigned n;
{
  register struct mhead *p;
  register unsigned int tocopy;
  register unsigned int nbytes;
  register int nunits;

  if ((p = (struct mhead *) mem) == 0)
    return malloc (n);
  p--;
  nunits = p -> mh_index;
  ASSERT (p -> mh_alloc == ISALLOC);

#ifdef rcheck
  ASSERT (p -> mh_magic4 == MAGIC4);
  {
    register char *m = mem + (tocopy = p -> mh_nbytes);
    ASSERT (*m++ == MAGIC1); ASSERT (*m++ == MAGIC1);
    ASSERT (*m++ == MAGIC1); ASSERT (*m   == MAGIC1);
  }
#else /* not rcheck */
  if (p -> mh_index >= 13)
    tocopy = (1 << (p -> mh_index + 3)) - sizeof *p;
  else
    tocopy = p -> mh_size;
#endif /* not rcheck */

  /* See if desired size rounds to same power of 2 as actual size. */
  nbytes = (n + sizeof *p + EXTRA + 7) & ~7;

  /* If ok, use the same block, just marking its size as changed.  */
  if (nbytes > (4 << nunits) && nbytes <= (8 << nunits))
    {
#ifdef rcheck
      register char *m = mem + tocopy;
      *m++ = 0;  *m++ = 0;  *m++ = 0;  *m++ = 0;
      p-> mh_nbytes = n;
      m = mem + n;
      *m++ = MAGIC1;  *m++ = MAGIC1;  *m++ = MAGIC1;  *m++ = MAGIC1;
#else /* not rcheck */
      p -> mh_size = n;
#endif /* not rcheck */
      return mem;
    }

  if (n < tocopy)
    tocopy = n;
  {
    register char *new;

    if ((new = malloc (n)) == 0)
      return 0;
    bcopy (mem, new, tocopy);
    free (mem);
    return new;
  }
}

/*
 * The following routines are not used and are left for documentation
 * purposes only.
 */

#ifdef NOTDEF
char *memalign ( alignment, size)
     unsigned alignment, size;
{
  register char *ptr = malloc (size + alignment);
  register char *aligned;
  register struct mhead *p;

  if (ptr == 0)
    return 0;
  /*
   * If entire block has the desired alignment, just accept it.
   */
  if (((int) ptr & (alignment - 1)) == 0)
    return ptr;
  /* Otherwise, get address of byte in the block that has that alignment.  */
  aligned = (char *) (((int) ptr + alignment - 1) & -alignment);
  /* Store a suitable indication of how to free the block,
     so that free can find the true beginning of it.  */
  p = (struct mhead *) aligned - 1;
  p -> mh_size = aligned - ptr;
  p -> mh_alloc = ISMEMALIGN;
  return aligned;
}

/* This runs into trouble with getpagesize on HPUX.
   Patching out seems cleaner than the ugly fix needed.
char *
valloc (size)
{
  return memalign (getpagesize (), size);
}
*/

get_lim_data ()
{
  struct rlimit XXrlimit;

  getrlimit (RLIMIT_DATA, &XXrlimit);
#ifdef RLIM_INFINITY
  lim_data = XXrlimit.rlim_cur & RLIM_INFINITY; /* soft limit */
#else
  lim_data = XXrlimit.rlim_cur;    /* soft limit */
#endif
}

#endif NOTDEF



/* dynamic memory allocation for GNU.
   Copyright (C) 1985, 1987 Free Software Foundation, Inc.

               NO WARRANTY

  BECAUSE THIS PROGRAM IS LICENSED FREE OF CHARGE, WE PROVIDE ABSOLUTELY
NO WARRANTY, TO THE EXTENT PERMITTED BY APPLICABLE STATE LAW.  EXCEPT
WHEN OTHERWISE STATED IN WRITING, FREE SOFTWARE FOUNDATION, INC,
RICHARD M. STALLMAN AND/OR OTHER PARTIES PROVIDE THIS PROGRAM "AS IS"
WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING,
BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY
AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE PROGRAM PROVE
DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR
CORRECTION.

 IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW WILL RICHARD M.
STALLMAN, THE FREE SOFTWARE FOUNDATION, INC., AND/OR ANY OTHER PARTY
WHO MAY MODIFY AND REDISTRIBUTE THIS PROGRAM AS PERMITTED BELOW, BE
LIABLE TO YOU FOR DAMAGES, INCLUDING ANY LOST PROFITS, LOST MONIES, OR
OTHER SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
USE OR INABILITY TO USE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR
DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY THIRD PARTIES OR
A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS) THIS
PROGRAM, EVEN IF YOU HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH
DAMAGES, OR FOR ANY CLAIM BY ANY OTHER PARTY.

        GENERAL PUBLIC LICENSE TO COPY

  1. You may copy and distribute verbatim copies of this source file
as you receive it, in any medium, provided that you conspicuously and
appropriately publish on each copy a valid copyright notice "Copyright
(C) 1985 Free Software Foundation, Inc."; and include following the
copyright notice a verbatim copy of the above disclaimer of warranty
and of this License.  You may charge a distribution fee for the
physical act of transferring a copy.

  2. You may modify your copy or copies of this source file or
any portion of it, and copy and distribute such modifications under
the terms of Paragraph 1 above, provided that you also do the following:

    a) cause the modified files to carry prominent notices stating
    that you changed the files and the date of any change; and

    b) cause the whole of any work that you distribute or publish,
    that in whole or in part contains or is a derivative of this
    program or any part thereof, to be licensed at no charge to all
    third parties on terms identical to those contained in this
    License Agreement (except that you may choose to grant more extensive
    warranty protection to some or all third parties, at your option).

    c) You may charge a distribution fee for the physical act of
    transferring a copy, and you may at your option offer warranty
    protection in exchange for a fee.

Mere aggregation of another unrelated program with this program (or its
derivative) on a volume of a storage or distribution medium does not bring
the other program under the scope of these terms.

  3. You may copy and distribute this program (or a portion or derivative
of it, under Paragraph 2) in object code or executable form under the terms
of Paragraphs 1 and 2 above provided that you also do one of the following:

    a) accompany it with the complete corresponding machine-readable
    source code, which must be distributed under the terms of
    Paragraphs 1 and 2 above; or,

    b) accompany it with a written offer, valid for at least three
    years, to give any third party free (except for a nominal
    shipping charge) a complete machine-readable copy of the
    corresponding source code, to be distributed under the terms of
    Paragraphs 1 and 2 above; or,

    c) accompany it with the information you received as to where the
    corresponding source code may be obtained.  (This alternative is
    allowed only for noncommercial distribution and only if you
    received the program in object code or executable form alone.)

For an executable file, complete source code means all the source code for
all modules it contains; but, as a special exception, it need not include
source code for modules which are standard libraries that accompany the
operating system on which the executable file runs.

  4. You may not copy, sublicense, distribute or transfer this program
except as expressly provided under this License Agreement.  Any attempt
otherwise to copy, sublicense, distribute or transfer this program is void and
your rights to use the program under this License agreement shall be
automatically terminated.  However, parties who have received computer
software programs from you with this License Agreement will not have
their licenses terminated so long as such parties remain in full compliance.

  5. If you wish to incorporate parts of this program into other free
programs whose distribution conditions are different, write to the Free
Software Foundation at 675 Mass Ave, Cambridge, MA 02139.  We have not yet
worked out a simple rule that can be stated here, but we will often permit
this.  We will be guided by the two goals of preserving the free status of
all derivatives of our free software and of promoting the sharing and reuse of
software.


In other words, you are welcome to use, share and improve this program.
You are forbidden to forbid anyone else to use, share and improve
what you give them.   Help stamp out software-hoarding!  */