hash.c: use rb_hash_* functions for objid_hash, double and ident.

Note, that ident becomes a bit slower, cause hash value is more "random".
New versions calculates fair hash value, and so provides statistically
fair collision rate.
Previous version relies on internal pattern of symbols and "usually" provides
lesser collisions. Though it could be compromised easely.

Author: funny-falcon

hash.c

@@ -175,8 +175,7 @@ any_hash(VALUE a, st_index_t (*other_func)(VALUE))
     }
     else if (BUILTIN_TYPE(a) == T_FLOAT) {
       flt:
-	hval = rb_dbl_hash(rb_float_value(a));
-	hnum = FIX2LONG(hval);
+	hnum = rb_dbl_hash_long(rb_float_value(a));
     }
     else {
 	hnum = other_func(a);
@@ -199,34 +198,29 @@ rb_any_hash(VALUE a)
     return any_hash(a, obj_any_hash);
 }
 
-static st_index_t
-rb_num_hash_start(st_index_t n)
+long
+rb_dbl_hash_long(double d)
 {
-    /*
-     * This hash function is lightly-tuned for Ruby.  Further tuning
-     * should be possible.  Notes:
-     *
-     * - (n >> 3) alone is great for heap objects and OK for fixnum,
-     *   however symbols perform poorly.
-     * - (n >> (RUBY_SPECIAL_SHIFT+3)) was added to make symbols hash well,
-     *   n.b.: +3 to remove most ID scope, +1 worked well initially, too
-     *   n.b.: +1 (instead of 3) worked well initially, too
-     * - (n << 16) was finally added to avoid losing bits for fixnums
-     * - avoid expensive modulo instructions, it is currently only
-     *   shifts and bitmask operations.
-     */
-    return (n >> (RUBY_SPECIAL_SHIFT + 3) ^ (n << 16)) ^ (n >> 3);
+    long hash;
+    unsigned i;
+#define ind_in_dbl type_roomof(double, st_index_t)
+    union {
+	st_index_t i[ind_in_dbl];
+	double d;
+    } v = { {0} };
+    /* normalize -0.0 to 0.0 */
+    v.d = d == 0.0 ? 0.0 : d;
+    hash = rb_hash_start(v.i[0]);
+    for (i = 1; i < ind_in_dbl; i++) {
+	hash = rb_hash_uint(hash, v.i[i]);
+    }
+    return rb_hash_end(hash);
 }
 
 long
 rb_objid_hash(st_index_t index)
 {
-    st_index_t hnum = rb_num_hash_start(index);
-
-    hnum = rb_hash_start(hnum);
-    hnum = rb_hash_uint(hnum, (st_index_t)rb_any_hash);
-    hnum = rb_hash_end(hnum);
-    return hnum;
+    return rb_hash_end(index);
 }
 
 static st_index_t
@@ -258,18 +252,7 @@ static const struct st_hash_type objhash = {
 static st_index_t
 rb_ident_hash(st_data_t n)
 {
-#ifdef USE_FLONUM /* RUBY */
-    /*
-     * - flonum (on 64-bit) is pathologically bad, mix the actual
-     *   float value in, but do not use the float value as-is since
-     *   many integers get interpreted as 2.0 or -2.0 [Bug #10761]
-     */
-    if (FLONUM_P(n)) {
-	n ^= (st_data_t)rb_float_value(n);
-    }
-#endif
-
-    return (st_index_t)rb_num_hash_start((st_index_t)n);
+    return rb_hash_end((st_index_t)n);
 }
 
 static const struct st_hash_type identhash = {

internal.h

@@ -1080,7 +1080,6 @@ struct st_table *rb_hash_tbl_raw(VALUE hash);
 VALUE rb_hash_has_key(VALUE hash, VALUE key);
 VALUE rb_hash_default_value(VALUE hash, VALUE key);
 VALUE rb_hash_set_default_proc(VALUE hash, VALUE proc);
-long rb_objid_hash(st_index_t index);
 st_table *rb_init_identtable(void);
 st_table *rb_init_identtable_with_size(st_index_t size);
 
@@ -1147,6 +1146,7 @@ VALUE rb_int_modulo(VALUE x, VALUE y);
 VALUE rb_int_round(VALUE num, int ndigits);
 VALUE rb_int2str(VALUE num, int base);
 VALUE rb_dbl_hash(double d);
+long  rb_dbl_hash_long(double d);
 VALUE rb_fix_plus(VALUE x, VALUE y);
 VALUE rb_int_ge(VALUE x, VALUE y);
 

numeric.c

@@ -1350,12 +1350,7 @@ flo_hash(VALUE num)
 VALUE
 rb_dbl_hash(double d)
 {
-    st_index_t hash;
-
-    /* normalize -0.0 to 0.0 */
-    if (d == 0.0) d = 0.0;
-    hash = rb_memhash(&d, sizeof(d));
-    return LONG2FIX(hash);
+    return LONG2FIX(rb_dbl_hash_long(d));
 }
 
 VALUE

object.c

@@ -162,15 +162,7 @@ rb_obj_equal(VALUE obj1, VALUE obj2)
 VALUE
 rb_obj_hash(VALUE obj)
 {
-    VALUE oid = rb_obj_id(obj);
-#if SIZEOF_LONG == SIZEOF_VOIDP
-    st_index_t index = NUM2LONG(oid);
-#elif SIZEOF_LONG_LONG == SIZEOF_VOIDP
-    st_index_t index = NUM2LL(oid);
-#else
-# error not supported
-#endif
-    return LONG2FIX(rb_objid_hash(index));
+    /* stub for documentation */
 }
 #else
 VALUE rb_obj_hash(VALUE obj);