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 /**
  * @file
  * Dynamic memory manager
  *
  * This is a lightweight replacement for the standard C library malloc().
  *
  * If you want to use the standard C library malloc() instead, define
  * MEM_LIBC_MALLOC to 1 in your lwipopts.h
  *
  * To let mem_malloc() use pools (prevents fragmentation and is much faster than
  * a heap but might waste some memory), define MEM_USE_POOLS to 1, define
  * MEM_USE_CUSTOM_POOLS to 1 and create a file "lwippools.h" that includes a list
  * of pools like this (more pools can be added between _START and _END):
  *
  * Define three pools with sizes 256, 512, and 1512 bytes
  * LWIP_MALLOC_MEMPOOL_START
  * LWIP_MALLOC_MEMPOOL(20, 256)
  * LWIP_MALLOC_MEMPOOL(10, 512)
  * LWIP_MALLOC_MEMPOOL(5, 1512)
  * LWIP_MALLOC_MEMPOOL_END
  */
 
 /*
  * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without modification,
  * are permitted provided that the following conditions are met:
  *
  * 1. Redistributions of source code must retain the above copyright notice,
  *    this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright notice,
  *    this list of conditions and the following disclaimer in the documentation
  *    and/or other materials provided with the distribution.
  * 3. The name of the author may not be used to endorse or promote products
  *    derived from this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
  * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
  * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
  * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
  * OF SUCH DAMAGE.
  *
  * This file is part of the lwIP TCP/IP stack.
  *
  * Author: Adam Dunkels <adam@sics.se>
  *         Simon Goldschmidt
  *
  */
 
 #include "lwip/opt.h"
 
 #if !MEM_LIBC_MALLOC /* don't build if not configured for use in lwipopts.h */
 
 #include "lwip/def.h"
 #include "lwip/mem.h"
 #include "lwip/sys.h"
 #include "lwip/stats.h"
 
 #include <string.h>
 
 #if MEM_USE_POOLS
 /* lwIP head implemented with different sized pools */
 
 /**
  * Allocate memory: determine the smallest pool that is big enough
  * to contain an element of 'size' and get an element from that pool.
  *
  * @param size the size in bytes of the memory needed
  * @return a pointer to the allocated memory or NULL if the pool is empty
  */
 void *
 mem_malloc(mem_size_t size)
 {
   struct memp_malloc_helper *element;
   memp_t poolnr;
   mem_size_t required_size = size + sizeof(struct memp_malloc_helper);
 
   for (poolnr = MEMP_POOL_FIRST; poolnr <= MEMP_POOL_LAST; poolnr++) {
 #if MEM_USE_POOLS_TRY_BIGGER_POOL
 again:
 #endif /* MEM_USE_POOLS_TRY_BIGGER_POOL */
     /* is this pool big enough to hold an element of the required size
        plus a struct memp_malloc_helper that saves the pool this element came from? */
     if (required_size <= memp_sizes[poolnr]) {
       break;
     }
   }
   if (poolnr > MEMP_POOL_LAST) {
     LWIP_ASSERT("mem_malloc(): no pool is that big!", 0);
     return NULL;
   }
   element = (struct memp_malloc_helper*)memp_malloc(poolnr);
   if (element == NULL) {
     /* No need to DEBUGF or ASSERT: This error is already
        taken care of in memp.c */
 #if MEM_USE_POOLS_TRY_BIGGER_POOL
     /** Try a bigger pool if this one is empty! */
     if (poolnr < MEMP_POOL_LAST) {
       poolnr++;
       goto again;
     }
 #endif /* MEM_USE_POOLS_TRY_BIGGER_POOL */
     return NULL;
   }
 
   /* save the pool number this element came from */
   element->poolnr = poolnr;
   /* and return a pointer to the memory directly after the struct memp_malloc_helper */
   element++;
 
   return element;
 }
 
 /**
  * Free memory previously allocated by mem_malloc. Loads the pool number
  * and calls memp_free with that pool number to put the element back into
  * its pool
  *
  * @param rmem the memory element to free
  */
 void
 mem_free(void *rmem)
 {
   struct memp_malloc_helper *hmem = (struct memp_malloc_helper*)rmem;
 
   LWIP_ASSERT("rmem != NULL", (rmem != NULL));
   LWIP_ASSERT("rmem == MEM_ALIGN(rmem)", (rmem == LWIP_MEM_ALIGN(rmem)));
 
   /* get the original struct memp_malloc_helper */
   hmem--;
 
   LWIP_ASSERT("hmem != NULL", (hmem != NULL));
   LWIP_ASSERT("hmem == MEM_ALIGN(hmem)", (hmem == LWIP_MEM_ALIGN(hmem)));
   LWIP_ASSERT("hmem->poolnr < MEMP_MAX", (hmem->poolnr < MEMP_MAX));
 
   /* and put it in the pool we saved earlier */
   memp_free(hmem->poolnr, hmem);
 }
 
 #else /* MEM_USE_POOLS */
 /* lwIP replacement for your libc malloc() */
 
 /**
  * The heap is made up as a list of structs of this type.
  * This does not have to be aligned since for getting its size,
  * we only use the macro SIZEOF_STRUCT_MEM, which automatically alignes.
  */
 struct mem {
   /** index (-> ram[next]) of the next struct */
   mem_size_t next;
   /** index (-> ram[next]) of the next struct */
   mem_size_t prev;
   /** 1: this area is used; 0: this area is unused */
   u8_t used;
 };
 
 /** All allocated blocks will be MIN_SIZE bytes big, at least!
  * MIN_SIZE can be overridden to suit your needs. Smaller values save space,
  * larger values could prevent too small blocks to fragment the RAM too much. */
 #ifndef MIN_SIZE
 #define MIN_SIZE             12
 #endif /* MIN_SIZE */
 /* some alignment macros: we define them here for better source code layout */
 #define MIN_SIZE_ALIGNED     LWIP_MEM_ALIGN_SIZE(MIN_SIZE)
 #define SIZEOF_STRUCT_MEM    LWIP_MEM_ALIGN_SIZE(sizeof(struct mem))
 #define MEM_SIZE_ALIGNED     LWIP_MEM_ALIGN_SIZE(MEM_SIZE)
 
 /** the heap. we need one struct mem at the end and some room for alignment */
 static u8_t ram_heap[MEM_SIZE_ALIGNED + (2*SIZEOF_STRUCT_MEM) + MEM_ALIGNMENT];
 /** pointer to the heap (ram_heap): for alignment, ram is now a pointer instead of an array */
 static u8_t *ram;
 /** the last entry, always unused! */
 static struct mem *ram_end;
 /** pointer to the lowest free block, this is used for faster search */
 static struct mem *lfree;
 
 /** concurrent access protection */
 static sys_sem_t mem_sem;
 
 #if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
 
 static volatile u8_t mem_free_count;
 
 /* Allow mem_free from other (e.g. interrupt) context */
 #define LWIP_MEM_FREE_DECL_PROTECT()  SYS_ARCH_DECL_PROTECT(lev_free)
 #define LWIP_MEM_FREE_PROTECT()       SYS_ARCH_PROTECT(lev_free)
 #define LWIP_MEM_FREE_UNPROTECT()     SYS_ARCH_UNPROTECT(lev_free)
 #define LWIP_MEM_ALLOC_DECL_PROTECT() SYS_ARCH_DECL_PROTECT(lev_alloc)
 #define LWIP_MEM_ALLOC_PROTECT()      SYS_ARCH_PROTECT(lev_alloc)
 #define LWIP_MEM_ALLOC_UNPROTECT()    SYS_ARCH_UNPROTECT(lev_alloc)
 
 #else /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
 
 /* Protect the heap only by using a semaphore */
 #define LWIP_MEM_FREE_DECL_PROTECT()
 #define LWIP_MEM_FREE_PROTECT()    sys_arch_sem_wait(mem_sem, 0)
 #define LWIP_MEM_FREE_UNPROTECT()  sys_sem_signal(mem_sem)
 /* mem_malloc is protected using semaphore AND LWIP_MEM_ALLOC_PROTECT */
 #define LWIP_MEM_ALLOC_DECL_PROTECT()
 #define LWIP_MEM_ALLOC_PROTECT()
 #define LWIP_MEM_ALLOC_UNPROTECT()
 
 #endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
 
 
 /**
  * "Plug holes" by combining adjacent empty struct mems.
  * After this function is through, there should not exist
  * one empty struct mem pointing to another empty struct mem.
  *
  * @param mem this points to a struct mem which just has been freed
  * @internal this function is only called by mem_free() and mem_realloc()
  *
  * This assumes access to the heap is protected by the calling function
  * already.
  */
 static void
 plug_holes(struct mem *mem)
 {
   struct mem *nmem;
   struct mem *pmem;
 
   LWIP_ASSERT("plug_holes: mem >= ram", (u8_t *)mem >= ram);
   LWIP_ASSERT("plug_holes: mem < ram_end", (u8_t *)mem < (u8_t *)ram_end);
   LWIP_ASSERT("plug_holes: mem->used == 0", mem->used == 0);
 
   /* plug hole forward */
   LWIP_ASSERT("plug_holes: mem->next <= MEM_SIZE_ALIGNED", mem->next <= MEM_SIZE_ALIGNED);
 
   nmem = (struct mem *)&ram[mem->next];
   if (mem != nmem && nmem->used == 0 && (u8_t *)nmem != (u8_t *)ram_end) {
     /* if mem->next is unused and not end of ram, combine mem and mem->next */
     if (lfree == nmem) {
       lfree = mem;
     }
     mem->next = nmem->next;
     ((struct mem *)&ram[nmem->next])->prev = (u8_t *)mem - ram;
   }
 
   /* plug hole backward */
   pmem = (struct mem *)&ram[mem->prev];
   if (pmem != mem && pmem->used == 0) {
     /* if mem->prev is unused, combine mem and mem->prev */
     if (lfree == mem) {
       lfree = pmem;
     }
     pmem->next = mem->next;
     ((struct mem *)&ram[mem->next])->prev = (u8_t *)pmem - ram;
   }
 }
 
 /**
  * Zero the heap and initialize start, end and lowest-free
  */
 void
 mem_init(void)
 {
   struct mem *mem;
 
   LWIP_ASSERT("Sanity check alignment",
     (SIZEOF_STRUCT_MEM & (MEM_ALIGNMENT-1)) == 0);
 
   /* align the heap */
   ram = LWIP_MEM_ALIGN(ram_heap);
   /* initialize the start of the heap */
   mem = (struct mem *)ram;
   mem->next = MEM_SIZE_ALIGNED;
   mem->prev = 0;
   mem->used = 0;
   /* initialize the end of the heap */
   ram_end = (struct mem *)&ram[MEM_SIZE_ALIGNED];
   ram_end->used = 1;
   ram_end->next = MEM_SIZE_ALIGNED;
   ram_end->prev = MEM_SIZE_ALIGNED;
 
   mem_sem = sys_sem_new(1);
 
   /* initialize the lowest-free pointer to the start of the heap */
   lfree = (struct mem *)ram;
 
   MEM_STATS_AVAIL(avail, MEM_SIZE_ALIGNED);
 }
 
 /**
  * Put a struct mem back on the heap
  *
  * @param rmem is the data portion of a struct mem as returned by a previous
  *             call to mem_malloc()
  */
 void
 mem_free(void *rmem)
 {
   struct mem *mem;
   LWIP_MEM_FREE_DECL_PROTECT();
 
   if (rmem == NULL) {
     LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("mem_free(p == NULL) was called.\n"));
     return;
   }
   LWIP_ASSERT("mem_free: sanity check alignment", (((mem_ptr_t)rmem) & (MEM_ALIGNMENT-1)) == 0);
 
   LWIP_ASSERT("mem_free: legal memory", (u8_t *)rmem >= (u8_t *)ram &&
     (u8_t *)rmem < (u8_t *)ram_end);
 
   if ((u8_t *)rmem < (u8_t *)ram || (u8_t *)rmem >= (u8_t *)ram_end) {
     SYS_ARCH_DECL_PROTECT(lev);
     LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_free: illegal memory\n"));
     /* protect mem stats from concurrent access */
     SYS_ARCH_PROTECT(lev);
     MEM_STATS_INC(illegal);
     SYS_ARCH_UNPROTECT(lev);
     return;
   }
   /* protect the heap from concurrent access */
   LWIP_MEM_FREE_PROTECT();
   /* Get the corresponding struct mem ... */
   mem = (struct mem *)((u8_t *)rmem - SIZEOF_STRUCT_MEM);
   /* ... which has to be in a used state ... */
   LWIP_ASSERT("mem_free: mem->used", mem->used);
   /* ... and is now unused. */
   mem->used = 0;
 
   if (mem < lfree) {
     /* the newly freed struct is now the lowest */
     lfree = mem;
   }
 
   MEM_STATS_DEC_USED(used, mem->next - ((u8_t *)mem - ram));
 
   /* finally, see if prev or next are free also */
   plug_holes(mem);
 #if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
   mem_free_count = 1;
 #endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
   LWIP_MEM_FREE_UNPROTECT();
 }
 
 /**
  * In contrast to its name, mem_realloc can only shrink memory, not expand it.
  * Since the only use (for now) is in pbuf_realloc (which also can only shrink),
  * this shouldn't be a problem!
  *
  * @param rmem pointer to memory allocated by mem_malloc the is to be shrinked
  * @param newsize required size after shrinking (needs to be smaller than or
  *                equal to the previous size)
  * @return for compatibility reasons: is always == rmem, at the moment
  *         or NULL if newsize is > old size, in which case rmem is NOT touched
  *         or freed!
  */
 void *
 mem_realloc(void *rmem, mem_size_t newsize)
 {
   mem_size_t size;
   mem_size_t ptr, ptr2;
   struct mem *mem, *mem2;
   /* use the FREE_PROTECT here: it protects with sem OR SYS_ARCH_PROTECT */
   LWIP_MEM_FREE_DECL_PROTECT();
 
   /* Expand the size of the allocated memory region so that we can
      adjust for alignment. */
   newsize = LWIP_MEM_ALIGN_SIZE(newsize);
 
   if(newsize < MIN_SIZE_ALIGNED) {
     /* every data block must be at least MIN_SIZE_ALIGNED long */
     newsize = MIN_SIZE_ALIGNED;
   }
 
   if (newsize > MEM_SIZE_ALIGNED) {
     return NULL;
   }
 
   LWIP_ASSERT("mem_realloc: legal memory", (u8_t *)rmem >= (u8_t *)ram &&
    (u8_t *)rmem < (u8_t *)ram_end);
 
   if ((u8_t *)rmem < (u8_t *)ram || (u8_t *)rmem >= (u8_t *)ram_end) {
     SYS_ARCH_DECL_PROTECT(lev);
     LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SEVERE, ("mem_realloc: illegal memory\n"));
     /* protect mem stats from concurrent access */
     SYS_ARCH_PROTECT(lev);
     MEM_STATS_INC(illegal);
     SYS_ARCH_UNPROTECT(lev);
     return rmem;
   }
   /* Get the corresponding struct mem ... */
   mem = (struct mem *)((u8_t *)rmem - SIZEOF_STRUCT_MEM);
   /* ... and its offset pointer */
   ptr = (u8_t *)mem - ram;
 
   size = mem->next - ptr - SIZEOF_STRUCT_MEM;
   LWIP_ASSERT("mem_realloc can only shrink memory", newsize <= size);
   if (newsize > size) {
     /* not supported */
     return NULL;
   }
   if (newsize == size) {
     /* No change in size, simply return */
     return rmem;
   }
 
   /* protect the heap from concurrent access */
   LWIP_MEM_FREE_PROTECT();
 
   MEM_STATS_DEC_USED(used, (size - newsize));
 
   mem2 = (struct mem *)&ram[mem->next];
   if(mem2->used == 0) {
     /* The next struct is unused, we can simply move it at little */
     mem_size_t next;
     /* remember the old next pointer */
     next = mem2->next;
     /* create new struct mem which is moved directly after the shrinked mem */
     ptr2 = ptr + SIZEOF_STRUCT_MEM + newsize;
     if (lfree == mem2) {
       lfree = (struct mem *)&ram[ptr2];
     }
     mem2 = (struct mem *)&ram[ptr2];
     mem2->used = 0;
     /* restore the next pointer */
     mem2->next = next;
     /* link it back to mem */
     mem2->prev = ptr;
     /* link mem to it */
     mem->next = ptr2;
     /* last thing to restore linked list: as we have moved mem2,
      * let 'mem2->next->prev' point to mem2 again. but only if mem2->next is not
      * the end of the heap */
     if (mem2->next != MEM_SIZE_ALIGNED) {
       ((struct mem *)&ram[mem2->next])->prev = ptr2;
     }
     /* no need to plug holes, we've already done that */
   } else if (newsize + SIZEOF_STRUCT_MEM + MIN_SIZE_ALIGNED <= size) {
     /* Next struct is used but there's room for another struct mem with
      * at least MIN_SIZE_ALIGNED of data.
      * Old size ('size') must be big enough to contain at least 'newsize' plus a struct mem
      * ('SIZEOF_STRUCT_MEM') with some data ('MIN_SIZE_ALIGNED').
      * @todo we could leave out MIN_SIZE_ALIGNED. We would create an empty
      *       region that couldn't hold data, but when mem->next gets freed,
      *       the 2 regions would be combined, resulting in more free memory */
     ptr2 = ptr + SIZEOF_STRUCT_MEM + newsize;
     mem2 = (struct mem *)&ram[ptr2];
     if (mem2 < lfree) {
       lfree = mem2;
     }
     mem2->used = 0;
     mem2->next = mem->next;
     mem2->prev = ptr;
     mem->next = ptr2;
     if (mem2->next != MEM_SIZE_ALIGNED) {
       ((struct mem *)&ram[mem2->next])->prev = ptr2;
     }
     /* the original mem->next is used, so no need to plug holes! */
   }
   /* else {
     next struct mem is used but size between mem and mem2 is not big enough
     to create another struct mem
     -> don't do anyhting. 
     -> the remaining space stays unused since it is too small
   } */
 #if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
   mem_free_count = 1;
 #endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
   LWIP_MEM_FREE_UNPROTECT();
   return rmem;
 }
 
 /**
  * Adam's mem_malloc() plus solution for bug #17922
  * Allocate a block of memory with a minimum of 'size' bytes.
  *
  * @param size is the minimum size of the requested block in bytes.
  * @return pointer to allocated memory or NULL if no free memory was found.
  *
  * Note that the returned value will always be aligned (as defined by MEM_ALIGNMENT).
  */
 void *
 mem_malloc(mem_size_t size)
 {
   mem_size_t ptr, ptr2;
   struct mem *mem, *mem2;
 #if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
   u8_t local_mem_free_count = 0;
 #endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
   LWIP_MEM_ALLOC_DECL_PROTECT();
 
   if (size == 0) {
     return NULL;
   }
 
   /* Expand the size of the allocated memory region so that we can
      adjust for alignment. */
   size = LWIP_MEM_ALIGN_SIZE(size);
 
   if(size < MIN_SIZE_ALIGNED) {
     /* every data block must be at least MIN_SIZE_ALIGNED long */
     size = MIN_SIZE_ALIGNED;
   }
 
   if (size > MEM_SIZE_ALIGNED) {
     return NULL;
   }
 
   /* protect the heap from concurrent access */
   sys_arch_sem_wait(mem_sem, 0);
   LWIP_MEM_ALLOC_PROTECT();
 #if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
   /* run as long as a mem_free disturbed mem_malloc */
   do {
     local_mem_free_count = 0;
 #endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
 
     /* Scan through the heap searching for a free block that is big enough,
      * beginning with the lowest free block.
      */
     for (ptr = (u8_t *)lfree - ram; ptr < MEM_SIZE_ALIGNED - size;
          ptr = ((struct mem *)&ram[ptr])->next) {
       mem = (struct mem *)&ram[ptr];
 #if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
       mem_free_count = 0;
       LWIP_MEM_ALLOC_UNPROTECT();
       /* allow mem_free to run */
       LWIP_MEM_ALLOC_PROTECT();
       if (mem_free_count != 0) {
         local_mem_free_count = mem_free_count;
       }
       mem_free_count = 0;
 #endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
 
       if ((!mem->used) &&
           (mem->next - (ptr + SIZEOF_STRUCT_MEM)) >= size) {
         /* mem is not used and at least perfect fit is possible:
          * mem->next - (ptr + SIZEOF_STRUCT_MEM) gives us the 'user data size' of mem */
 
         if (mem->next - (ptr + SIZEOF_STRUCT_MEM) >= (size + SIZEOF_STRUCT_MEM + MIN_SIZE_ALIGNED)) {
           /* (in addition to the above, we test if another struct mem (SIZEOF_STRUCT_MEM) containing
            * at least MIN_SIZE_ALIGNED of data also fits in the 'user data space' of 'mem')
            * -> split large block, create empty remainder,
            * remainder must be large enough to contain MIN_SIZE_ALIGNED data: if
            * mem->next - (ptr + (2*SIZEOF_STRUCT_MEM)) == size,
            * struct mem would fit in but no data between mem2 and mem2->next
            * @todo we could leave out MIN_SIZE_ALIGNED. We would create an empty
            *       region that couldn't hold data, but when mem->next gets freed,
            *       the 2 regions would be combined, resulting in more free memory
            */
           ptr2 = ptr + SIZEOF_STRUCT_MEM + size;
           /* create mem2 struct */
           mem2 = (struct mem *)&ram[ptr2];
           mem2->used = 0;
           mem2->next = mem->next;
           mem2->prev = ptr;
           /* and insert it between mem and mem->next */
           mem->next = ptr2;
           mem->used = 1;
 
           if (mem2->next != MEM_SIZE_ALIGNED) {
             ((struct mem *)&ram[mem2->next])->prev = ptr2;
           }
           MEM_STATS_INC_USED(used, (size + SIZEOF_STRUCT_MEM));
         } else {
           /* (a mem2 struct does no fit into the user data space of mem and mem->next will always
            * be used at this point: if not we have 2 unused structs in a row, plug_holes should have
            * take care of this).
            * -> near fit or excact fit: do not split, no mem2 creation
            * also can't move mem->next directly behind mem, since mem->next
            * will always be used at this point!
            */
           mem->used = 1;
           MEM_STATS_INC_USED(used, mem->next - ((u8_t *)mem - ram));
         }
 
         if (mem == lfree) {
           /* Find next free block after mem and update lowest free pointer */
           while (lfree->used && lfree != ram_end) {
             LWIP_MEM_ALLOC_UNPROTECT();
             /* prevent high interrupt latency... */
             LWIP_MEM_ALLOC_PROTECT();
             lfree = (struct mem *)&ram[lfree->next];
           }
           LWIP_ASSERT("mem_malloc: !lfree->used", ((lfree == ram_end) || (!lfree->used)));
         }
         LWIP_MEM_ALLOC_UNPROTECT();
         sys_sem_signal(mem_sem);
         LWIP_ASSERT("mem_malloc: allocated memory not above ram_end.",
          (mem_ptr_t)mem + SIZEOF_STRUCT_MEM + size <= (mem_ptr_t)ram_end);
         LWIP_ASSERT("mem_malloc: allocated memory properly aligned.",
          ((mem_ptr_t)mem + SIZEOF_STRUCT_MEM) % MEM_ALIGNMENT == 0);
         LWIP_ASSERT("mem_malloc: sanity check alignment",
           (((mem_ptr_t)mem) & (MEM_ALIGNMENT-1)) == 0);
 
         return (u8_t *)mem + SIZEOF_STRUCT_MEM;
       }
     }
 #if LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT
     /* if we got interrupted by a mem_free, try again */
   } while(local_mem_free_count != 0);
 #endif /* LWIP_ALLOW_MEM_FREE_FROM_OTHER_CONTEXT */
   LWIP_DEBUGF(MEM_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("mem_malloc: could not allocate %"S16_F" bytes\n", (s16_t)size));
   MEM_STATS_INC(err);
   LWIP_MEM_ALLOC_UNPROTECT();
   sys_sem_signal(mem_sem);
   return NULL;
 }
 
 #endif /* MEM_USE_POOLS */
 /**
  * Contiguously allocates enough space for count objects that are size bytes
  * of memory each and returns a pointer to the allocated memory.
  *
  * The allocated memory is filled with bytes of value zero.
  *
  * @param count number of objects to allocate
  * @param size size of the objects to allocate
  * @return pointer to allocated memory / NULL pointer if there is an error
  */
 void *mem_calloc(mem_size_t count, mem_size_t size)
 {
   void *p;
 
   /* allocate 'count' objects of size 'size' */
   p = mem_malloc(count * size);
   if (p) {
     /* zero the memory */
     memset(p, 0, count * size);
   }
   return p;
 }
 
 #endif /* !MEM_LIBC_MALLOC */