/* -*-c-*-
*
- * $Id: mpx-kmul.c,v 1.2 1999/12/11 10:58:02 mdw Exp $
+ * $Id: mpx-kmul.c,v 1.3 1999/12/13 15:35:01 mdw Exp $
*
* Karatsuba's multiplication algorithm
*
/*----- Revision history --------------------------------------------------*
*
* $Log: mpx-kmul.c,v $
+ * Revision 1.3 1999/12/13 15:35:01 mdw
+ * Simplify and improve.
+ *
* Revision 1.2 1999/12/11 10:58:02 mdw
* Remove tweakable comments.
*
/*----- Header files ------------------------------------------------------*/
+#include <assert.h>
#include <stdio.h>
#include "mpx.h"
avm = avl;
}
- /* --- Sort out the middle term --- *
- *
- * I'm going to keep track of the carry by hand rather than pass it down to
- * the next level, because it means multiplication by one or zero, which I
- * can do easily myself.
- */
+ 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 --- */
{
- unsigned f = 0;
- enum {
- carry_a = 1,
- carry_b = 2
- };
-
- mpw *bsv = sv + m, *ssv = bsv + m;
- mpw *rdv = dv + m, *rdvl = rdv + 2 * m;
-
- UADD2(sv, bsv + 1, av, avm, avm, avl);
- if (*bsv)
- f |= carry_a;
- UADD2(bsv, ssv + 1, bv, bvm, bvm, bvl);
- if (*ssv)
- f |= carry_b;
- MPX_ZERO(dv, rdv);
+ mpw *bsv = sv + m + 1, *ssv = bsv + m + 1;
+ mpw *rdv = dv + m, *rdvl = rdv + 2 * (m + 2);
+
+ UADD2(sv, bsv, av, avm, avm, avl);
+ UADD2(bsv, ssv, bv, bvm, bvm, bvl);
if (m > KARATSUBA_CUTOFF)
mpx_kmul(rdv, rdvl, sv, bsv, bsv, ssv, ssv, svl);
else
mpx_umul(rdv, rdvl, sv, bsv, bsv, ssv);
- MPX_ZERO(rdvl, dvl);
- rdv += m; rdvl += m;
- if (f & carry_b)
- UADD(rdv, sv, bsv);
- if (f & carry_a)
- UADD(rdv, bsv, ssv);
- if (!(~f & (carry_a | carry_b)))
- MPX_UADDN(rdv + m, rdvl, 1);
}
/* --- Sort out the other two terms --- */
{
- mpw *ssv = sv + 2 * m;
+ mpw *svm = sv + m, *svn = svm + m, *ssv = svn + 4;
mpw *tdv = dv + m;
mpw *rdv = tdv + m;
- if (m > KARATSUBA_CUTOFF)
- mpx_kmul(sv, ssv, avm, avl, bvm, bvl, ssv, svl);
- else
- mpx_umul(sv, ssv, avm, avl, bvm, bvl);
- UADD(rdv, sv, ssv);
- USUB(tdv, sv, ssv);
-
+ if (avl == avm || bvl == bvm)
+ MPX_ZERO(rdv + m + 1, dvl);
+ else {
+ if (m > KARATSUBA_CUTOFF)
+ mpx_kmul(sv, ssv, avm, avl, bvm, bvl, ssv, svl);
+ else
+ mpx_umul(sv, ssv, avm, avl, bvm, bvl);
+ MPX_COPY(rdv + m + 1, dvl, svm + 1, svn);
+ UADD(rdv, sv, svm + 1);
+ USUB(tdv, sv, svn);
+ }
+
if (m > KARATSUBA_CUTOFF)
mpx_kmul(sv, ssv, av, avm, bv, bvm, ssv, svl);
else
mpx_umul(sv, ssv, av, avm, bv, bvm);
- USUB(tdv, sv, ssv);
- UADD(dv, sv, ssv);
+ MPX_COPY(dv, tdv, sv, svm);
+ USUB(tdv, sv, svn);
+ UADD(tdv, svm, svn);
}
}