tracking_collisions.c: initial skeleton.

... of a program to just test the hashing functions collisions on a 24
bit output with strings that are very likely Redis key names, and names
of a kind that are particularly prone to collisions.

utils/tracking_collisions.c

@@ -0,0 +1,40 @@
+/* This is a small program used in order to understand the collison rate
+ * of CRC64 (ISO version) VS other stronger hashing functions in the context
+ * of hashing keys for the Redis "tracking" feature (client side caching
+ * assisted by the server).
+ *
+ * The program attempts to hash keys with common names in the form of
+ *
+ *  prefix:<counter>
+ *
+ * And counts the resulting collisons generated in the 24 bits of output
+ * needed for the tracking feature invalidation table (16 millions + entries)
+ *
+ * --------------------------------------------------------------------------
+ *
+ * Copyright (C) 2019 Salvatore Sanfilippo
+ * This code is released under the BSD 2 clause license.
+ */
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+#include <stdio.h>
+
+#define TABLE_SIZE (1<<24)
+int Table[TABLE_SIZE];
+
+/* Test the hashing function provided as callback and return the
+ * number of collisions found. */
+unsigned long testHashingFunction(uint64_t (*hash)(char *, size_t)) {
+    unsigned long collisions = 0;
+    memset(Table,0,sizeof(Table));
+    char *prefixes[] = {"object", "message", "user", NULL};
+    return collisions;
+}
+
+int main(void) {
+    printf("SHA1 : %lu\n", testHashingFunction(sha1Hash));
+    printf("CRC64: %lu\n", testHashingFunction(crc64Hash));
+    return 0;
+}