+static bool
+check_tuning (Hash_table *table)
+{
+ const Hash_tuning *tuning = table->tuning;
+ float epsilon;
+ if (tuning == &default_tuning)
+ return true;
+
+ /* Be a bit stricter than mathematics would require, so that
+ rounding errors in size calculations do not cause allocations to
+ fail to grow or shrink as they should. The smallest allocation
+ is 11 (due to next_prime's algorithm), so an epsilon of 0.1
+ should be good enough. */
+ epsilon = 0.1f;
+
+ if (epsilon < tuning->growth_threshold
+ && tuning->growth_threshold < 1 - epsilon
+ && 1 + epsilon < tuning->growth_factor
+ && 0 <= tuning->shrink_threshold
+ && tuning->shrink_threshold + epsilon < tuning->shrink_factor
+ && tuning->shrink_factor <= 1
+ && tuning->shrink_threshold + epsilon < tuning->growth_threshold)
+ return true;
+
+ table->tuning = &default_tuning;
+ return false;
+}
+
+/* Compute the size of the bucket array for the given CANDIDATE and
+ TUNING, or return 0 if there is no possible way to allocate that
+ many entries. */
+
+static size_t
+compute_bucket_size (size_t candidate, const Hash_tuning *tuning)
+{
+ if (!tuning->is_n_buckets)
+ {
+ float new_candidate = candidate / tuning->growth_threshold;
+ if (SIZE_MAX <= new_candidate)
+ return 0;
+ candidate = new_candidate;
+ }
+ candidate = next_prime (candidate);
+ if (xalloc_oversized (candidate, sizeof (struct hash_entry *)))
+ return 0;
+ return candidate;
+}
+
+/* Allocate and return a new hash table, or NULL upon failure. The initial
+ number of buckets is automatically selected so as to _guarantee_ that you
+ may insert at least CANDIDATE different user entries before any growth of
+ the hash table size occurs. So, if have a reasonably tight a-priori upper
+ bound on the number of entries you intend to insert in the hash table, you
+ may save some table memory and insertion time, by specifying it here. If
+ the IS_N_BUCKETS field of the TUNING structure is true, the CANDIDATE
+ argument has its meaning changed to the wanted number of buckets.
+
+ TUNING points to a structure of user-supplied values, in case some fine
+ tuning is wanted over the default behavior of the hasher. If TUNING is
+ NULL, the default tuning parameters are used instead. If TUNING is
+ provided but the values requested are out of bounds or might cause
+ rounding errors, return NULL.
+
+ The user-supplied HASHER function, when not NULL, accepts two
+ arguments ENTRY and TABLE_SIZE. It computes, by hashing ENTRY contents, a
+ slot number for that entry which should be in the range 0..TABLE_SIZE-1.
+ This slot number is then returned.
+
+ The user-supplied COMPARATOR function, when not NULL, accepts two
+ arguments pointing to user data, it then returns true for a pair of entries
+ that compare equal, or false otherwise. This function is internally called
+ on entries which are already known to hash to the same bucket index,
+ but which are distinct pointers.
+
+ The user-supplied DATA_FREER function, when not NULL, may be later called
+ with the user data as an argument, just before the entry containing the
+ data gets freed. This happens from within `hash_free' or `hash_clear'.
+ You should specify this function only if you want these functions to free
+ all of your `data' data. This is typically the case when your data is
+ simply an auxiliary struct that you have malloc'd to aggregate several
+ values. */