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Diff for /embedaddon/libiconv/srclib/malloca.c between versions 1.1.1.2 and 1.1.1.3

version 1.1.1.2, 2012/05/29 09:29:43 version 1.1.1.3, 2021/03/17 13:38:46
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 /* Safe automatic memory allocation.  /* Safe automatic memory allocation.
   Copyright (C) 2003, 2006-2007, 2009-2011 Free Software Foundation, Inc.   Copyright (C) 2003, 2006-2007, 2009-2019 Free Software Foundation, Inc.
   Written by Bruno Haible <bruno@clisp.org>, 2003.   Written by Bruno Haible <bruno@clisp.org>, 2003, 2018.
   
    This program is free software; you can redistribute it and/or modify     This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by     it under the terms of the GNU General Public License as published by
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    GNU General Public License for more details.     GNU General Public License for more details.
   
    You should have received a copy of the GNU General Public License     You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software Foundation,   along with this program; if not, see <https://www.gnu.org/licenses/>.  */
   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */ 
   
 #define _GL_USE_STDLIB_ALLOC 1  #define _GL_USE_STDLIB_ALLOC 1
 #include <config.h>  #include <config.h>
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 /* The speed critical point in this file is freea() applied to an alloca()  /* The speed critical point in this file is freea() applied to an alloca()
    result: it must be fast, to match the speed of alloca().  The speed of     result: it must be fast, to match the speed of alloca().  The speed of
    mmalloca() and freea() in the other case are not critical, because they     mmalloca() and freea() in the other case are not critical, because they
   are only invoked for big memory sizes.  */   are only invoked for big memory sizes.
    Here we use a bit in the address as an indicator, an idea by Ondřej Bílka.
    malloca() can return three types of pointers:
      - Pointers ≡ 0 mod 2*sa_alignment_max come from stack allocation.
      - Pointers ≡ sa_alignment_max mod 2*sa_alignment_max come from heap
        allocation.
      - NULL comes from a failed heap allocation.  */
   
#if HAVE_ALLOCA/* Type for holding very small pointer differences.  */
 typedef unsigned char small_t;
 /* Verify that it is wide enough.  */
 verify (2 * sa_alignment_max - 1 <= (small_t) -1);
   
 /* Store the mmalloca() results in a hash table.  This is needed to reliably  
    distinguish a mmalloca() result and an alloca() result.  
   
    Although it is possible that the same pointer is returned by alloca() and  
    by mmalloca() at different times in the same application, it does not lead  
    to a bug in freea(), because:  
      - Before a pointer returned by alloca() can point into malloc()ed memory,  
        the function must return, and once this has happened the programmer must  
        not call freea() on it anyway.  
      - Before a pointer returned by mmalloca() can point into the stack, it  
        must be freed.  The only function that can free it is freea(), and  
        when freea() frees it, it also removes it from the hash table.  */  
   
 #define MAGIC_NUMBER 0x1415fb4a  
 #define MAGIC_SIZE sizeof (int)  
 /* This is how the header info would look like without any alignment  
    considerations.  */  
 struct preliminary_header { void *next; char room[MAGIC_SIZE]; };  
 /* But the header's size must be a multiple of sa_alignment_max.  */  
 #define HEADER_SIZE \  
   (((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max)  
 struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; };  
 verify (HEADER_SIZE == sizeof (struct header));  
 /* We make the hash table quite big, so that during lookups the probability  
    of empty hash buckets is quite high.  There is no need to make the hash  
    table resizable, because when the hash table gets filled so much that the  
    lookup becomes slow, it means that the application has memory leaks.  */  
 #define HASH_TABLE_SIZE 257  
 static void * mmalloca_results[HASH_TABLE_SIZE];  
   
 #endif  
   
 void *  void *
 mmalloca (size_t n)  mmalloca (size_t n)
 {  {
 #if HAVE_ALLOCA  #if HAVE_ALLOCA
  /* Allocate one more word, that serves as an indicator for malloc()ed  /* Allocate one more word, used to determine the address to pass to freea(),
     memory, so that freea() of an alloca() result is fast.  */     and room for the alignment ≡ sa_alignment_max mod 2*sa_alignment_max.  */
  size_t nplus = n + HEADER_SIZE;  size_t nplus = n + sizeof (small_t) + 2 * sa_alignment_max - 1;
   
   if (nplus >= n)    if (nplus >= n)
     {      {
      char *p = (char *) malloc (nplus);      char *mem = (char *) malloc (nplus);
   
      if (p != NULL)      if (mem != NULL)
         {          {
          size_t slot;          char *p =
            (char *)((((uintptr_t)mem + sizeof (small_t) + sa_alignment_max - 1)
          p += HEADER_SIZE;                      & ~(uintptr_t)(2 * sa_alignment_max - 1))
                     + sa_alignment_max);
          /* Put a magic number into the indicator word.  */          /* Here p >= mem + sizeof (small_t),
          ((int *) p)[-1] = MAGIC_NUMBER;             and p <= mem + sizeof (small_t) + 2 * sa_alignment_max - 1
             hence p + n <= mem + nplus.
          /* Enter p into the hash table.  */             So, the memory range [p, p+n) lies in the allocated memory range
          slot = (unsigned long) p % HASH_TABLE_SIZE;             [mem, mem + nplus).  */
          ((struct header *) (p - HEADER_SIZE))->next = mmalloca_results[slot];          ((small_t *) p)[-1] = p - mem;
          mmalloca_results[slot] = p;          /* p ≡ sa_alignment_max mod 2*sa_alignment_max.  */
 
           return p;            return p;
         }          }
     }      }
Line 107  mmalloca (size_t n) Line 82  mmalloca (size_t n)
 void  void
 freea (void *p)  freea (void *p)
 {  {
  /* mmalloca() may have returned NULL.  */  /* Check argument.  */
  if (p != NULL)  if ((uintptr_t) p & (sa_alignment_max - 1))
     {      {
      /* Attempt to quickly distinguish the mmalloca() result - which has      /* p was not the result of a malloca() call.  Invalid argument.  */
         a magic indicator word - and the alloca() result - which has an      abort ();
         uninitialized indicator word.  It is for this test that sa_increment 
         additional bytes are allocated in the alloca() case.  */ 
      if (((int *) p)[-1] == MAGIC_NUMBER) 
        { 
          /* Looks like a mmalloca() result.  To see whether it really is one, 
             perform a lookup in the hash table.  */ 
          size_t slot = (unsigned long) p % HASH_TABLE_SIZE; 
          void **chain = &mmalloca_results[slot]; 
          for (; *chain != NULL;) 
            { 
              if (*chain == p) 
                { 
                  /* Found it.  Remove it from the hash table and free it.  */ 
                  char *p_begin = (char *) p - HEADER_SIZE; 
                  *chain = ((struct header *) p_begin)->next; 
                  free (p_begin); 
                  return; 
                } 
              chain = &((struct header *) ((char *) *chain - HEADER_SIZE))->next; 
            } 
        } 
      /* At this point, we know it was not a mmalloca() result.  */ 
     }      }
     /* Determine whether p was a non-NULL pointer returned by mmalloca().  */
     if ((uintptr_t) p & sa_alignment_max)
       {
         void *mem = (char *) p - ((small_t *) p)[-1];
         free (mem);
       }
 }  }
 #endif  #endif
   
   /*
    * Hey Emacs!
    * Local Variables:
    * coding: utf-8
    * End:
    */
Removed from v.1.1.1.2  
changed lines
  Added in v.1.1.1.3

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