Sun Mar 12 02:13:29 PM CET 2023

src/generic_lru_cache.md

@@ -0,0 +1,51 @@
+Title: Generic LRU Cache in C
+Author: Alessandro Mauri
+
+# Generic LRU Cache in C
+I've been working on an immediate mode gui library and for the renderer I took
+inspiration from Casey Muratori's [refterm][rt] for the font rendering.
+Doing so I needed to implement a hash map and a LRU cache in top of it, so I did
+and took the time to write a macro abomination in order to make it type generic.
+
+Well in reality since I made it to store font glyphs it uses `uint32_t`s for keys
+but it can be easily extended to use strings since the underlying hash map is 
+type generic as well.
+So here they are:
+
+- [hash map][hm]
+- [LRU cache][ch]
+
+Usage:
+
+```
+/* Declare the cache, hash_u32 and hash_cmp_u32 are ready-made functions in 
+ * generic_hash.h */
+#include "generic_cache.h"
+static inline unsigned int hash(unsigned int code)
+{
+	// identity map the ascii range
+	return code < 128 ? code : hash_u32(code);
+}
+CACHE_DECL(cache, struct font_glyph, hash, hash_cmp_u32)
+
+/* Initialize the cache */
+struct cache c = cache_init(); // CACHE_SIZE is constant
+
+/* Searching from in the cache */
+const struct font_glyph *r;
+unsigned int code = 'F';
+if ((r = cache_search(&c, code)) != NULL) {
+	// ...
+}
+
+/* Inserting is a bit different, you first find an open (unused) spot and then
+ * you provide it to cache_insert() */
+struct font_glyph g = {.codepoint = 'a', ...};
+unsigned int spot = cache_get(&c);
+cache_insert(&c, &g, 'a', spot);
+
+```
+
+[rt]: https://github.com/cmuratori/refterm
+[hm]: https://git.alemauri.eu/alema/ugui/src/branch/master/text_rendering/generic_hash.h
+[ch]: https://git.alemauri.eu/alema/ugui/src/branch/master/text_rendering/generic_cache.h