bb

text_rendering/hash.c

@@ -0,0 +1,76 @@
+#define _POSIX_C_SOURCE 200809l
+#define _DEFAULT_SOURCE
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "hash.h"
+
+#define MAXSIZE 4096
+
+
+static unsigned int hash(unsigned int code)
+{
+	// identity map the ascii range
+	if (code < 128) return code;
+	return (uint32_t)((uint64_t)(code*2654435761)>>32);
+}
+
+
+struct hm_ref * hm_create(unsigned int size)
+{
+	if (!size || size > MAXSIZE)
+		return NULL;
+
+	// round to the greater power of two
+	size = 1<<__builtin_clz(size);
+
+	// FIXME: check for intger overflow here
+	struct hm_ref *h = malloc(sizeof(struct hm_ref)+sizeof(struct hm_entry)*size);
+	if (h) {
+		h->items = 0;
+		h->size  = size;
+		memset(h->bucket, 0, sizeof(struct hm_ref)*size);
+	}
+	return h;
+}
+
+
+void hm_destroy(struct hm_ref *hm)
+{
+	free(hm);
+}
+
+
+static struct hm_entry * lookup(struct hm_ref *hm, unsigned int code)
+{
+	// fast modulo operation for power-of-2 size
+	unsigned int mask = hm->size - 1;
+	unsigned int i = hash(code);
+	for (unsigned int j = 1; ; i += j++) {
+		if (!hm->bucket[i&mask].code || hm->bucket[i].code == code)
+			return &(hm->bucket[i&mask]);
+	}
+	return NULL;
+}
+
+
+struct hm_entry * hm_search(struct hm_ref *hm, unsigned int code)
+{
+	struct hm_entry *r = lookup(hm, code);
+	if (r) {
+		if (r->code == code)
+			return r;
+		return NULL;
+	}
+	return r;
+}
+
+
+struct hm_entry * hm_insert(struct hm_ref *hm, struct hm_entry *entry)
+{
+	struct hm_entry *r = lookup(hm, entry->code);
+	if (r) *r = *entry;
+	return r;
+}