Fix bounds on workspace for Karatsuba operations.

[u/mdw/catacomb] / mpx-kmul.c

diff --git a/mpx-kmul.c b/mpx-kmul.c
index f6b0b4f..1981a28 100644 (file)
--- a/mpx-kmul.c
+++ b/mpx-kmul.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: mpx-kmul.c,v 1.7 2000/10/08 15:48:35 mdw Exp $
+ * $Id: mpx-kmul.c,v 1.8 2002/10/09 00:36:03 mdw Exp $
  *
  * Karatsuba's multiplication algorithm
  *
@@ -30,6 +30,9 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: mpx-kmul.c,v $
+ * Revision 1.8  2002/10/09 00:36:03  mdw
+ * Fix bounds on workspace for Karatsuba operations.
+ *
  * Revision 1.7  2000/10/08 15:48:35  mdw
  * Rename Karatsuba constants now that we have @gfx_kmul@ too.
  *
@@ -66,7 +69,7 @@
 
 #ifdef TEST_RIG
 #  undef MPK_THRESH
-#  define MPK_THRESH 2
+#  define MPK_THRESH 4                 /* Smallest possible correct value */
 #endif
 
 /*----- Main code ---------------------------------------------------------*/
@@ -85,9 +88,9 @@
  *             multiplication (e.g., @mpx_umul@) on large numbers, although
  *             more expensive on small ones.
  *
- *             The destination must be twice as large as the larger
- *             argument.  The scratch space must be twice as large as the
- *             larger argument, plus the magic number @MPK_SLOP@.
+ *             The destination must be three times as large as the larger
+ *             argument.  The scratch space must be five times as large as
+ *             the larger argument.
  */
 
 void mpx_kmul(mpw *dv, mpw *dvl,
@@ -149,17 +152,14 @@ void mpx_kmul(mpw *dv, mpw *dvl,
       avm = avl;
   }
 
-  assert(((void)"Destination too small for Karatsuba multiply",
-         dvl - dv >= 4 * m));
-  assert(((void)"Not enough workspace for Karatsuba multiply",
-         svl - sv >= 4 * m));
-
   /* --- Sort out the middle term --- */
 
   {
     mpw *bsv = sv + m + 1, *ssv = bsv + m + 1;
     mpw *rdv = dv + m, *rdvl = rdv + 2 * (m + 2);
 
+    assert(rdvl < dvl);
+    assert(ssv < svl);
     UADD2(sv, bsv, av, avm, avm, avl);
     UADD2(bsv, ssv, bv, bvm, bvm, bvl);
     if (m > MPK_THRESH)
@@ -246,8 +246,8 @@ static int umul(dstr *v)
   LOAD(b, bl, &v[1]);
   LOAD(c, cl, &v[2]);
   m = MAX(al - a, bl - b) + 1;
-  ALLOC(d, dl, 2 * m);
-  ALLOC(s, sl, 2 * m + 32);
+  ALLOC(d, dl, 3 * m);
+  ALLOC(s, sl, 5 * m);
 
   mpx_kmul(d, dl, a, al, b, bl, s, sl);
   if (!mpx_ueq(d, dl, c, cl)) {