It is possible to replace the core memory management functions used by the ASN1C run-time memory manager. This has the advantage of preserving the existing management scheme but with the use of different core functions. Using different core functions may be necessary on some systems that do not have the standard C run-time functions malloc, free, and realloc, or when extra functionality is desired.

To replace the core functions, use the rtxMemSetAllocFuncs runtime library call:

   void rtxMemSetAllocFuncs (OSMallocFunc malloc_func, OSReallocFunc
      realloc_func, OSFreeFunc free_func);

The malloc, realloc, and free functions must have the same prototype as the standard C functions. Some systems do not have a realloc-like function. In this case, realloc_func may be set to NULL. This will cause the malloc_func/free_func pair to be used to do reallocations.

This function must be called before the context initialization function (rtInitContext) because context initialization requires low level memory management facilities be in place in order to do its work.

Note that this function makes use of static global memory to hold the function definitions. This type of memory is not available in all run-time environments (most notably Symbian). In this case, an alternative function is provided for setting the memory functions. This function is rtxInitContextExt, which must be called in place of the standard context initialization function (rtInitContext). In this case, there is a bit more work required to initialize a context because the ASN.1 subcontext must be manually initialized. This is an example of the code required to do this:

   int stat = rtxInitContextExt (pctxt, malloc_func, realloc_func,
      free_func);

   if (0 == stat) {
      /* Add ASN.1 error codes to global table */
      rtErrASN1Init ();

      /* Init ASN.1 info block */
      stat = rtCtxtInitASN1Info (pctxt);
   }

Memory management can also be tuned by setting the default memory heap block size. The way memory management works is that a large block of memory is allocated up front on the first memory management call. This block is then subdivided on subsequent calls until the memory is used up. A new block is then started. The default value is 4K (4096) bytes. The value can be set lower for space constrained systems and higher to improve performance in systems that have sufficient memory resources. To set the block size, the following run-time function should be used: void rtxMemSetDefBlkSize (OSUINT32 blkSize);

This function must be called prior to context initialization.