233 lines
6 KiB
C++
233 lines
6 KiB
C++
/*
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* memory.h
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*
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* Copyright (c) 1993 - 1995 by DataBeam Corporation, Lexington, KY
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*
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* Abstract:
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* This is the interface file for the Memory class. Instances of this
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* class are used to pass data around the system.
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*
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* Each instance of this class maintains two pointers. The first is a
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* pointer to the reference data (or the source data) which this object
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* is responsible for representing. The second is a pointer to a copy
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* buffer, which is a piece of allocated memory that a Memory object
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* can copy the data into if necessary.
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*
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* When a Memory object is created, both of these addresses are passed
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* in to it. It does not, however, copy the data from the reference
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* buffer to the copy buffer just yet. If anyone asks the address of the
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* buffer, it will simply return the reference pointer. However, the
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* first time the buffer is locked, the data will be copied from the
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* reference buffer to the copy buffer for safe keeping. In essence,
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* the lock function tells the Memory object that someone is interested
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* in the data for longer than the reference buffer will remain valid.
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*
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* After the object is locked, a call to retrieve a memory pointer will
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* result in the copy pointer being returned.
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*
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* Each time the lock function is called, a lock count is incremented.
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* The copy operation only takes place the first time the buffer is
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* locked, however.
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*
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* In addition to maintaining a lock count, this object keeps a flag
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* indicating whether or not it has been freed by the allocator. This
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* freeing really means that the object is enabled to be freed as soon
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* as the lock count hits zero.
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*
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* Caveats:
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* None.
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*
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* Author:
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* James P. Galvin, Jr.
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*/
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#ifndef _MEMORY2_H_
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#define _MEMORY2_H_
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/*
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* FreeStack
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* This is a list container that can be used to hold memory addresses.
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* This structure is used to keep information about each free stack. There
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* is one free stack for each size block being maintained by each memory
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* manager.
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*/
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typedef struct
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{
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ULong block_size;
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ULong total_block_count;
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ULong current_block_count;
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ULong block_stack_offset;
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} FreeStack;
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typedef FreeStack * PFreeStack;
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/*
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* This type is used to represent a block number in the memory manager. This
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* is essentially an index used to uniquely identify each block being
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* maintained by an instance of this class.
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*/
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typedef ULong BlockNumber;
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typedef BlockNumber * PBlockNumber;
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#define INVALID_BLOCK_NUMBER 0xffffffffL
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/*
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* This type is used to determine when a memory object should be destroyed.
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* When a memory object is created, this field is set by the owner. The owner
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* can then ask for the value of this field at any time to help determine when
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* the object should be destroyed. Essentially, this field indicates whether
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* the global lock count for the memory this object represents should be used
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* to determine when this object should be destroyed.
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*/
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typedef enum
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{
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MEMORY_LOCK_NORMAL,
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MEMORY_LOCK_IGNORED
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} MemoryLockMode;
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/*
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* This is the class definition for the Memory class.
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*/
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class Memory;
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typedef Memory * PMemory;
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class Memory
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{
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public:
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Memory (PUChar reference_ptr,
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ULong length,
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PUChar copy_ptr,
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BlockNumber block_number,
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MemoryLockMode memory_lock_mode);
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virtual ~Memory () { };
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PUChar GetPointer ()
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{
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return (Copy_Ptr);
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}
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ULong GetLength ()
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{
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return (Length);
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}
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BlockNumber GetBlockNumber ()
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{
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return (Block_Number);
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}
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MemoryLockMode GetMemoryLockMode ()
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{
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return (Memory_Lock_Mode);
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}
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private:
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ULong Length;
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PUChar Copy_Ptr;
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BlockNumber Block_Number;
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MemoryLockMode Memory_Lock_Mode;
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};
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/*
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* Memory (
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* PUChar reference_ptr,
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* ULong length,
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* PUChar copy_ptr,
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* PFreeStack free_stack,
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* BlockNumber block_number)
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*
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* Functional Description:
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* This is the constructor for the Memory class. All it does is
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* initialize the instance variable with the passed in values.
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*
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* Formal Parameters:
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* reference_ptr (i)
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* This is a pointer to the data that is to represented by this
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* Memory object.
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* length (i)
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* This is the length of the reference buffer.
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* copy_ptr (i)
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* This is the address of an allocated buffer that the Memory object
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* can use to preserve the contents of the reference buffer if a lock
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* operation occurs.
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* free_stack (i)
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* This is a pointer to a list container that the allocated memory
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* block came from. This field is not used internally, and is only
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* held here in order to improve the performance of the memory
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* manager that is using Memory objects.
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* block_number (i)
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* This is the block number for the memory block that is represented
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* by this object. This field is not used internally, and is only
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* held here in order to improve the performance of the memory
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* manager that is using Memory objects.
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*
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* Return Value:
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* None.
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*
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* Side Effects:
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* None.
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*
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* Caveats:
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* None.
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*/
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/*
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* ~Memory ()
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*
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* Functional Description:
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* This is the destructor for the Memory class. It does nothing at this
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* time. Note that it is the responsibility of the memory manager that
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* is using Memory objects to free up the memory.
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*
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* Formal Parameters:
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* None.
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*
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* Return Value:
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* None.
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*
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* Side Effects:
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* None.
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*
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* Caveats:
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* None.
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*/
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/*
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* ULong GetLength ()
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*
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* Functional Description:
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* This function retrieves the length of the data being represented by
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* this object.
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*
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* Formal Parameters:
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* None.
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*
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* Return Value:
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* The length of the data.
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*
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* Side Effects:
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* None.
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*
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* Caveats:
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* None.
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*/
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/*
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* BlockNumber GetBlockNumber ()
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*
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* Functional Description:
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* This function retrieves the block number of the block that is being
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* represented by this object. This allows the memory manager to put the
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* memory block back into the stack very efficiently.
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*
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* Formal Parameters:
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* None.
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*
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* Return Value:
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* The block number of the internal memory block.
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*
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* Side Effects:
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* None.
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*
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* Caveats:
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* None.
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*/
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#endif
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