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/*
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=======================================================================
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Cache for out-of-core octree.
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Uses an LRU page replacement scheme. Page table nodes are stored in
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order of reference in a doubly linked list, with the most recently used
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(MRU) page at the head, and the least recently used (LRU) at the tail.
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Nodes are referenced by the page's base address via a hashtable for
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constant time access (in the absence of hash collisions). Hash
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collisions can be limited by adjusting the hashtable load factor
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OOC_CACHE_LOAD; this is the fraction of the number of pages that will
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actually be cached.
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Roland Schregle (roland.schregle@{hslu.ch, gmail.com})
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(c) Lucerne University of Applied Sciences and Arts,
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supported by the Swiss National Science Foundation (SNSF, #147053)
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=======================================================================
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$Id: ooccache.h,v 1.13 2015/11/16 13:33:08 taschreg Exp taschreg $
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*/
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#ifndef OOC_CACHE_H
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#define OOC_CACHE_H
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#include <stdio.h>
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#include <stdint.h>
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/* Hashtable load factor to limit hash collisions */
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#define OOC_CACHE_LOAD 0.75
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/* Minimum number of cache pages */
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#define OOC_CACHE_MINPAGES 8
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/* Hashing function for key -> pagetable mapping (assumes n is prime) */
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#define OOC_CACHE_PRIME 19603
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#define OOC_CACHE_HASH(k,n) ((k) * OOC_CACHE_PRIME % (n))
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/* Next index in pagetable probe sequence for collision resolution */
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#define OOC_CACHE_NEXT(i,n) (((i) + 1) % (n))
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/* Cache key and index types */
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typedef uint32_t OOC_CacheKey;
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typedef uint32_t OOC_CacheIdx;
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/* Undefined value for cache index */
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#define OOC_CACHEIDX_NULL UINT32_MAX
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typedef struct {
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OOC_CacheKey key; /* Key to resolve hashing collisions */
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OOC_CacheIdx prev, next; /* Previous/next page in history */
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void *data; /* Start of page data */
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} OOC_CacheNode;
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typedef struct {
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unsigned recSize, /* Data record size in bytes */
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recPerPage; /* Page size in number of records */
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unsigned long pageSize; /* Page size in bytes (precomp) */
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OOC_CacheIdx pageCnt, /* Num pages used */
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numPages; /* Pagetable size */
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/* NOTE: The hashtable load factor limits the number of pages actually
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* used, such that pageCnt <= OOC_CACHE_LOAD * numPages */
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OOC_CacheNode *pageTable; /* Pagetable with numPages nodes */
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OOC_CacheIdx mru, lru; /* Most/least recently used page
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== head/tail of page history */
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OOC_CacheKey lastKey; /* Previous key to detect repeat lookups */
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OOC_CacheNode *lastPage; /* Previous page for repeat lookups */
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unsigned long numReads, /* Statistics counters */
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numHits,
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numColl,
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numRept;
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} OOC_Cache;
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/* Initialise cache containing up to numPages pages; this is rounded up
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* the next prime number to reduce hash clustering and collisions. The
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* page size recPerPage is specified in units of records of size recSize
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* bytes. Returns 0 on success, else -1. */
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int OOC_CacheInit (OOC_Cache *cache, unsigned numPages,
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unsigned recPerPage, unsigned recSize);
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/* Return pointer to cached record with index recIdx, loading from file
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* and possibly evicting the LRU page */
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void *OOC_CacheData (OOC_Cache *cache, FILE *file, unsigned long recIdx);
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/* Delete cache and free allocated pages */
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void OOC_DeleteCache (OOC_Cache *cache);
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#endif
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