Add documentation for double_hash().

[adu.git] / adu.c

diff --git a/adu.c b/adu.c
index 8c84c82639e57f57549652fae3ac0aa4123d2789..8068d205f2274dded3074158a105243bb4de1b11 100644 (file)
--- a/adu.c
+++ b/adu.c
@@ -2,6 +2,7 @@
 #include <dirent.h> /* readdir() */
 
 #include "gcc-compat.h"
+#include "cmdline.h"
 #include "osl.h"
 #include "fd.h"
 #include "hash.h"
@@ -13,6 +14,9 @@ DEFINE_ERRLIST;
 #define DATABASE_DIR "/tmp/adu"
 #define UID_LIST DATABASE_DIR "/" "uid_list"
 
+/** Command line and config file options. */
+static struct gengetopt_args_info conf;
+
 struct user_info {
        uint32_t uid;
        struct osl_table *table;
@@ -44,7 +48,7 @@ __printf_2_3 void __log(int ll, const char* fmt,...)
        time_t t1;
        char str[255] = "";
 
-       if (ll < 4)
+       if (ll < conf.loglevel_arg)
                return;
        outfd = stderr;
        time(&t1);
@@ -295,7 +299,22 @@ static int create_tables(void)
        return 1;
 }
 
-
+/*
+ * We use a hash table of size s=2^uid_hash_bits to map the uids into the
+ * interval [0..s]. Hash collisions are treated by open addressing, i.e.
+ * unused slots in the table are used to store different uids that hash to the
+ * same slot.
+ *
+ * If a hash collision occurs, different slots are successively probed in order
+ * to find an unused slot for the new uid. Probing is implemented via a second
+ * hash function that maps the uid to h=(uid * PRIME2) | 1, which is always an
+ * odd number.
+ *
+ * An odd number is sufficient to make sure each entry of the hash table gets
+ * probed for probe_num between 0 and s-1 because s is a power of two, hence
+ * the second hash value never hash a common divisor with the hash table size.
+ * IOW: h is invertible in the ring [0..s].
+ */
 static uint32_t double_hash(uint32_t uid, uint32_t probe_num)
 {
        return (uid * PRIME1 + ((uid * PRIME2) | 1) * probe_num)
@@ -746,7 +765,7 @@ static void close_all_tables(void)
        free_hash_table();
 }
 
-static int com_create(char *dirname)
+static int com_create()
 {
        int ret = create_tables();
        if (ret < 0)
@@ -754,7 +773,7 @@ static int com_create(char *dirname)
        ret = open_dir_table();
        if (ret < 0)
                return ret;
-       ret = scan_dir(dirname);
+       ret = scan_dir(conf.base_dir_arg);
        if (ret < 0)
                goto out;
        ret = write_uid_list();
@@ -806,13 +825,21 @@ static int com_select(void)
 
 int main(int argc, char **argv)
 {
-       int ret = -E_SYNTAX;
-       if (argc > 2)
-               goto out;
-       if (argc == 1)
+       int ret;
+       struct cmdline_parser_params params = {
+               .override = 0,
+               .initialize = 1,
+               .check_required = 0,
+               .check_ambiguity = 0,
+               .print_errors = 1
+       };
+
+       cmdline_parser_ext(argc, argv, &conf, &params); /* aborts on errors */
+       ret = -E_SYNTAX;
+       if (conf.select_given)
                ret = com_select();
        else
-               ret = com_create(argv[1]);
+               ret = com_create();
        if (ret < 0)
                goto out;
 out: