From:	"Mark E." <snowball3 AT bigfoot DOT com>
To:	djgpp-workers AT delorie DOT com
Date:	Thu, 17 May 2001 15:17:27 -0400
MIME-Version:	1.0
Subject:	realloc enhancement
Message-ID:	<3B03EB87.15564.BB69E@localhost>
X-mailer:	Pegasus Mail for Win32 (v3.12c)
Reply-To:	djgpp-workers AT delorie DOT com

This patch enhances realloc by trying to extend the allocated block before
allocating a new one. How does it look?

Note that I had to change a word to get this note through.

Index: malloc.c
===================================================================
RCS file: /cvs/djgpp/djgpp/src/libc/ansi/stdlib/malloc.c,v
retrieving revision 1.8
diff -c -p -r1.8 malloc.c
*** malloc.c	2001/01/20 04:09:57	1.8
--- malloc.c	2001/05/17 17:26:54
*************** free(void *ptr)
*** 316,321 ****
--- 316,388 ----
    CHECK(block);
  }
  
+ /* delete block of memory from the free list.  */
+ static inline void
+ delete_freelist (BLOCK *b)
+ {
+   int bu = b2bucket (b);
+   BLOCK *bp, **bpp;
+ 
+   bpp = freelist + bu;
+   for (bp = freelist[bu]; bp; bp = bp->next)
+   {
+     if (bp == b)
+     {
+       *bpp = bp->next;
+       break;
+     }
+   }
+ }
+ 
+ /* Insert block of memory into free list.  */
+ static inline void
+ insert_freelist (BLOCK *b)
+ {
+  int bu = b2bucket (b);
+  b->next = freelist[bu];
+  freelist[bu] = b;
+ }
+ 
+ /* Try to increase the size of the allocated block. */
+ static BLOCK *
+ realloc_inplace (BLOCK *cur, size_t old_size, size_t new_size)
+ {
+   BLOCK *after;
+   size_t after_sz, delta;
+ 
+   after = AFTER(cur);
+   after_sz = after->size;
+ 
+   /* Fail if the block following the one being extended is in use.  */
+   if (after_sz & 1)
+     return NULL;
+ 
+   /* Size of block increase.  */
+   delta = new_size - old_size;
+ 
+   /* Fail if the free block is not large enough.  */
+   if (delta > after_sz)
+     return NULL;
+ 
+   /* delete block from free list.  */
+   delete_freelist(after);
+ 
+   /* Trim extra space from the free block when its large enough
+      to make a new block.  */
+   if (after_sz - delta >= 16)
+   {
+     BLOCK *after2 = split_block(after, delta + 8);
+     /* Add trimmed block to free list.  */
+     insert_freelist(after2);
+   }
+ 
+   /* Merge the two blocks.  */
+   cur->size += after->size + 8;
+   ENDSZ(cur) = cur->size;
+ 
+   return cur;
+ }
+ 
  void *
  realloc(void *ptr, size_t size)
  {
*************** realloc(void *ptr, size_t size)
*** 337,342 ****
--- 404,413 ----
        return ptr;
      copysize = size;
    }
+ 
+   /* Try to increase the size of the allocation.  */
+   if (realloc_inplace (b, copysize, size))
+     return ptr;
  
    newptr = (char *)malloc(size);
  #if DEBUG

- Raw text -