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src/generic_lru_cache.md
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src/generic_lru_cache.md
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Title: Generic LRU Cache in C
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Author: Alessandro Mauri
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# Generic LRU Cache in C
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I've been working on an immediate mode gui library and for the renderer I took
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inspiration from Casey Muratori's [refterm][rt] for the font rendering.
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Doing so I needed to implement a hash map and a LRU cache in top of it, so I did
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and took the time to write a macro abomination in order to make it type generic.
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Well in reality since I made it to store font glyphs it uses `uint32_t`s for keys
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but it can be easily extended to use strings since the underlying hash map is
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type generic as well.
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So here they are:
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- [hash map][hm]
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- [LRU cache][ch]
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Usage:
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```
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/* Declare the cache, hash_u32 and hash_cmp_u32 are ready-made functions in
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* generic_hash.h */
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#include "generic_cache.h"
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static inline unsigned int hash(unsigned int code)
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{
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// identity map the ascii range
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return code < 128 ? code : hash_u32(code);
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}
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CACHE_DECL(cache, struct font_glyph, hash, hash_cmp_u32)
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/* Initialize the cache */
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struct cache c = cache_init(); // CACHE_SIZE is constant
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/* Searching from in the cache */
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const struct font_glyph *r;
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unsigned int code = 'F';
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if ((r = cache_search(&c, code)) != NULL) {
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// ...
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}
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/* Inserting is a bit different, you first find an open (unused) spot and then
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* you provide it to cache_insert() */
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struct font_glyph g = {.codepoint = 'a', ...};
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unsigned int spot = cache_get(&c);
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cache_insert(&c, &g, 'a', spot);
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```
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[rt]: https://github.com/cmuratori/refterm
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[hm]: https://git.alemauri.eu/alema/ugui/src/branch/master/text_rendering/generic_hash.h
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[ch]: https://git.alemauri.eu/alema/ugui/src/branch/master/text_rendering/generic_cache.h
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