fix flonum hashing regression from r45384

* st.c (st_numhash): mix float value for flonum
* hash.c (rb_any_hash): ditto
* benchmark/bm_hash_aref_flo.rb: new benchmark
* benchmark/bm_hash_ident_flo.rb: ditto
  [Bug ruby#10761]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49376 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Author: normal

ChangeLog

@@ -1,3 +1,11 @@
+Thu Jan 22 16:45:24 2015  Eric Wong  <[email protected]>
+
+	* st.c (st_numhash): mix float value for flonum
+	* hash.c (rb_any_hash): ditto
+	* benchmark/bm_hash_aref_flo.rb: new benchmark
+	* benchmark/bm_hash_ident_flo.rb: ditto
+	  [Bug #10761]
+
 Wed Jan 21 22:33:51 2015  Akinori MUSHA  <[email protected]>
 
 	* misc/ruby-electric.el: Import version 2.2.1 from

benchmark/bm_hash_aref_flo.rb

@@ -0,0 +1,4 @@
+h = {}
+strs = (1..10000).to_a.map!(&:to_f)
+strs.each { |s| h[s] = s }
+50.times { strs.each { |s| h[s] } }

benchmark/bm_hash_ident_flo.rb

@@ -0,0 +1,4 @@
+h = {}.compare_by_identity
+strs = (1..10000).to_a.map!(&:to_f)
+strs.each { |s| h[s] = s }
+50.times { strs.each { |s| h[s] } }

hash.c

@@ -137,7 +137,13 @@ rb_any_hash(VALUE a)
 
     if (SPECIAL_CONST_P(a)) {
 	if (a == Qundef) return 0;
-	if (STATIC_SYM_P(a)) a >>= (RUBY_SPECIAL_SHIFT + ID_SCOPE_SHIFT);
+	if (STATIC_SYM_P(a)) {
+	    a >>= (RUBY_SPECIAL_SHIFT + ID_SCOPE_SHIFT);
+	}
+	else if (FLONUM_P(a)) {
+	    /* prevent pathological behavior: [Bug #10761] */
+	    a = (st_index_t)rb_float_value(a);
+	}
 	hnum = rb_objid_hash((st_index_t)a);
     }
     else if (BUILTIN_TYPE(a) == T_STRING) {

st.c

@@ -1761,6 +1761,15 @@ st_numhash(st_data_t n)
      * - (n << 3) was finally added to avoid losing bits for fixnums
      * - avoid expensive modulo instructions, it is currently only
      *   shifts and bitmask operations.
+     * - 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]
      */
+#ifdef USE_FLONUM /* RUBY */
+    if (FLONUM_P(n)) {
+	n ^= (st_data_t)rb_float_value(n);
+    }
+#endif
+
     return (st_index_t)((n>>(RUBY_SPECIAL_SHIFT+3)|(n<<3)) ^ (n>>3));
 }