From: Nobuyoshi Nakada <nobu@...>
Date: 2008-03-02T00:29:10+09:00
Subject: Re: Ruby String hash key overflow when converting to Fixnum.

Hi,

At Sat, 1 Mar 2008 23:50:37 +0900,
Chiyuan Zhang wrote in [ruby-core:15713]:
> Another more efficient way is to perform truncation when calculating
> String hash to make the result meet what we geet in Ruby world. Here's
> the patch:

Then, shouldn't all results be in the Fixnum range?


Index: hash.c
===================================================================
--- hash.c	(revision 15666)
+++ hash.c	(working copy)
@@ -76,13 +76,14 @@ rb_any_hash(VALUE a)
 {
     VALUE hval;
+    int hnum;
 
     switch (TYPE(a)) {
       case T_FIXNUM:
       case T_SYMBOL:
-	return (int)a;
+	hnum = (int)a;
 	break;
 
       case T_STRING:
-	return rb_str_hash(a);
+	hnum = rb_str_hash(a);
 	break;
 
@@ -92,6 +93,8 @@ rb_any_hash(VALUE a)
 	    hval = rb_funcall(hval, '%', 1, INT2FIX(536870923));
 	}
-	return (int)FIX2LONG(hval);
+	hnum = (int)FIX2LONG(hval);
     }
+    hnum <<= 1;
+    return RSHIFT(hnum, 1);
 }
 


-- 
Nobu Nakada