--- /dev/null
+/* mpn_bz_divrem_n and auxilliary routines.
+
+ THE FUNCTIONS IN THIS FILE ARE INTERNAL FUNCTIONS WITH MUTABLE
+ INTERFACES. IT IS ONLY SAFE TO REACH THEM THROUGH DOCUMENTED INTERFACES.
+ IN FACT, IT IS ALMOST GUARANTEED THAT THEY'LL CHANGE OR DISAPPEAR IN A
+ FUTURE GNU MP RELEASE.
+
+
+Copyright (C) 2000 Free Software Foundation, Inc.
+Contributed by Paul Zimmermann.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or (at your
+option) any later version.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library; see the file COPYING.LIB. If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+/*
+[1] Fast Recursive Division, by Christoph Burnikel and Joachim Ziegler,
+ Technical report MPI-I-98-1-022, october 1998.
+ http://www.mpi-sb.mpg.de/~ziegler/TechRep.ps.gz
+*/
+
+static mp_limb_t mpn_bz_div_3_halves_by_2
+ _PROTO ((mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n));
+
+
+/* mpn_bz_divrem_n(n) calls 2*mul(n/2)+2*div(n/2), thus to be faster than
+ div(n) = 4*div(n/2), we need mul(n/2) to be faster than the classic way,
+ i.e. n/2 >= KARATSUBA_MUL_THRESHOLD */
+#ifndef BZ_THRESHOLD
+#define BZ_THRESHOLD (7 * KARATSUBA_MUL_THRESHOLD)
+#endif
+
+#if 0
+static
+unused_mpn_divrem (qp, qxn, np, nn, dp, dn)
+ mp_ptr qp;
+ mp_size_t qxn;
+ mp_ptr np;
+ mp_size_t nn;
+ mp_srcptr dp;
+ mp_size_t dn;
+{
+ /* This might be useful: */
+ if (qxn != 0)
+ {
+ mp_limb_t c;
+ mp_ptr tp = alloca ((nn + qxn) * BYTES_PER_MP_LIMB);
+ MPN_COPY (tp + qxn - nn, np, nn);
+ MPN_ZERO (tp, qxn);
+ c = mpn_divrem (qp, 0L, tp, nn + qxn, dp, dn);
+ /* Maybe copy proper part of tp to np? Documentation is unclear about
+ the returned np value when qxn != 0 */
+ return c;
+ }
+}
+#endif
+
+
+/* mpn_bz_divrem_n - Implements algorithm of page 8 in [1]: divides (np,2n)
+ by (dp,n) and puts the quotient in (qp,n), the remainder in (np,n).
+ Returns most significant limb of the quotient, which is 0 or 1.
+ Requires that the most significant bit of the divisor is set. */
+
+mp_limb_t
+#if __STDC__
+mpn_bz_divrem_n (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n)
+#else
+mpn_bz_divrem_n (qp, np, dp, n)
+ mp_ptr qp;
+ mp_ptr np;
+ mp_srcptr dp;
+ mp_size_t n;
+#endif
+{
+ mp_limb_t qhl, cc;
+
+ if (n % 2 != 0)
+ {
+ qhl = mpn_bz_divrem_n (qp + 1, np + 2, dp + 1, n - 1);
+ cc = mpn_submul_1 (np + 1, qp + 1, n - 1, dp[0]);
+ cc = mpn_sub_1 (np + n, np + n, 1, cc);
+ if (qhl) cc += mpn_sub_1 (np + n, np + n, 1, dp[0]);
+ while (cc)
+ {
+ qhl -= mpn_sub_1 (qp + 1, qp + 1, n - 1, (mp_limb_t) 1);
+ cc -= mpn_add_n (np + 1, np + 1, dp, n);
+ }
+ qhl += mpn_add_1 (qp + 1, qp + 1, n - 1,
+ mpn_sb_divrem_mn (qp, np, n + 1, dp, n));
+ }
+ else
+ {
+ mp_size_t n2 = n/2;
+ qhl = mpn_bz_div_3_halves_by_2 (qp + n2, np + n2, dp, n2);
+ qhl += mpn_add_1 (qp + n2, qp + n2, n2,
+ mpn_bz_div_3_halves_by_2 (qp, np, dp, n2));
+ }
+ return qhl;
+}
+
+
+/* divides (np, 3n) by (dp, 2n) and puts the quotient in (qp, n),
+ the remainder in (np, 2n) */
+
+static mp_limb_t
+#if __STDC__
+mpn_bz_div_3_halves_by_2 (mp_ptr qp, mp_ptr np, mp_srcptr dp, mp_size_t n)
+#else
+mpn_bz_div_3_halves_by_2 (qp, np, dp, n)
+ mp_ptr qp;
+ mp_ptr np;
+ mp_srcptr dp;
+ mp_size_t n;
+#endif
+{
+ mp_size_t twon = n + n;
+ mp_limb_t qhl, cc;
+ mp_ptr tmp;
+ TMP_DECL (marker);
+
+ TMP_MARK (marker);
+ if (n < BZ_THRESHOLD)
+ qhl = mpn_sb_divrem_mn (qp, np + n, twon, dp + n, n);
+ else
+ qhl = mpn_bz_divrem_n (qp, np + n, dp + n, n);
+ tmp = (mp_ptr) TMP_ALLOC (twon * BYTES_PER_MP_LIMB);
+ mpn_mul_n (tmp, qp, dp, n);
+ cc = mpn_sub_n (np, np, tmp, twon);
+ TMP_FREE (marker);
+ if (qhl) cc += mpn_sub_n (np + n, np + n, dp, n);
+ while (cc)
+ {
+ qhl -= mpn_sub_1 (qp, qp, n, (mp_limb_t) 1);
+ cc -= mpn_add_n (np, np, dp, twon);
+ }
+ return qhl;
+}
projects / ghc-hetmet.git / blobdiff