shyouhei	2018-11-15 14:10:40 +0900 (Thu, 15 Nov 2018)

  New Revision: 65734

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=65734

  Log:
    bignum.c: ee should be signed
    
    In C, signed + unsigned of the same size results in unsigned (cf:
    ISO/IEC 9899:1990 section 6.2.1.5). However `num` is signed here.
    Which means the addition must be done in signed.

  Modified files:
    trunk/bignum.c
Index: bignum.c
===================================================================
--- bignum.c	(revision 65733)
+++ bignum.c	(revision 65734)
@@ -1511,15 +1511,16 @@ bigdivrem_mulsub(BDIGIT *zds, size_t zn, https://github.com/ruby/ruby/blob/trunk/bignum.c#L1511
     i = 0;
 
     do {
-        BDIGIT_DBL ee;
+        BDIGIT_DBL_SIGNED ee;
         t2 += (BDIGIT_DBL)yds[i] * x;
         ee = num - BIGLO(t2);
-        num = (BDIGIT_DBL)zds[i] + ee;
+        num = (BDIGIT_DBL_SIGNED)zds[i] + ee;
         if (ee) zds[i] = BIGLO(num);
         num = BIGDN(num);
         t2 = BIGDN(t2);
     } while (++i < yn);
-    num += zds[i] - t2; /* borrow from high digit; don't update */
+    num -= (BDIGIT_DBL_SIGNED)t2;
+    num += (BDIGIT_DBL_SIGNED)zds[yn]; /* borrow from high digit; don't update */
     return num;
 }
 

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