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/** |
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* \addtogroup exampleapps |
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* @{ |
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*/ |
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/** |
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* \file |
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* Memory block allocation routines. |
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* \author Adam Dunkels <adam@sics.se> |
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* |
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* The memory block allocation routines provide a simple yet powerful |
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* set of functions for managing a set of memory blocks of fixed |
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* size. A set of memory blocks is statically declared with the |
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* MEMB() macro. Memory blocks are allocated from the declared |
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* memory by the memb_alloc() function, and are deallocated with the |
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* memb_free() function. |
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* |
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* \note Because of namespace clashes only one MEMB() can be |
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* declared per C module, and the name scope of a MEMB() memory |
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* block is local to each C module. |
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* |
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* The following example shows how to declare and use a memory block |
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* called "cmem" which has 8 chunks of memory with each memory chunk |
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* being 20 bytes large. |
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* |
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\code |
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MEMB(cmem, 20, 8); |
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int main(int argc, char *argv[]) { |
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char *ptr; |
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memb_init(&cmem); |
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ptr = memb_alloc(&cmem); |
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if(ptr != NULL) { |
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do_something(ptr); |
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} else { |
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printf("Could not allocate memory.\n"); |
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} |
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if(memb_free(ptr) == 0) { |
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printf("Deallocation succeeded.\n"); |
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} |
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} |
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\endcode |
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* |
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*/ |
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#include <string.h> |
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#include "memb.h" |
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/*------------------------------------------------------------------------------*/ |
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/** |
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* Initialize a memory block that was declared with MEMB(). |
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* |
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* \param m A memory block previosly declared with MEMB(). |
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*/ |
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/*------------------------------------------------------------------------------*/ |
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void |
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memb_init(struct memb_blocks *m) |
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{ |
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memset(m->mem, (m->size + 1) * m->num, 0); |
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} |
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/*------------------------------------------------------------------------------*/ |
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/** |
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* Allocate a memory block from a block of memory declared with MEMB(). |
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* |
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* \param m A memory block previosly declared with MEMB(). |
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*/ |
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/*------------------------------------------------------------------------------*/ |
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char * |
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memb_alloc(struct memb_blocks *m) |
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{ |
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int i; |
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char *ptr; |
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ptr = m->mem; |
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for(i = 0; i < m->num; ++i) { |
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if(*ptr == 0) { |
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/* If this block was unused, we increase the reference count to |
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indicate that it now is used and return a pointer to the |
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first byte following the reference counter. */ |
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++*ptr; |
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return ptr + 1; |
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} |
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ptr += m->size + 1; |
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} |
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/* No free block was found, so we return NULL to indicate failure to |
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allocate block. */ |
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return NULL; |
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} |
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/*------------------------------------------------------------------------------*/ |
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/** |
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* Deallocate a memory block from a memory block previously declared |
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* with MEMB(). |
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* |
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* \param m m A memory block previosly declared with MEMB(). |
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* |
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* \param ptr A pointer to the memory block that is to be deallocated. |
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* |
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* \return The new reference count for the memory block (should be 0 |
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* if successfully deallocated) or -1 if the pointer "ptr" did not |
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* point to a legal memory block. |
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*/ |
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/*------------------------------------------------------------------------------*/ |
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char |
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memb_free(struct memb_blocks *m, char *ptr) |
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{ |
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int i; |
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char *ptr2; |
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/* Walk through the list of blocks and try to find the block to |
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which the pointer "ptr" points to. */ |
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ptr2 = m->mem; |
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for(i = 0; i < m->num; ++i) { |
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if(ptr2 == ptr - 1) { |
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/* We've found to block to which "ptr" points so we decrease the |
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reference count and return the new value of it. */ |
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return --*ptr2; |
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} |
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ptr2 += m->size + 1; |
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} |
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return -1; |
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} |
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/*------------------------------------------------------------------------------*/ |
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/** |
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* Increase the reference count for a memory chunk. |
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* |
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* \note No sanity checks are currently made. |
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* |
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* \param m m A memory block previosly declared with MEMB(). |
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* |
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* \param ptr A pointer to the memory chunk for which the reference |
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* count should be increased. |
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* |
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* \return The new reference count. |
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*/ |
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/*------------------------------------------------------------------------------*/ |
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char |
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memb_ref(struct memb_blocks *m, char *ptr) |
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{ |
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return ++*(ptr - 1); |
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} |
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/*------------------------------------------------------------------------------*/ |
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