--- /dev/null
+/* mpn_divrem_1 -- mpn by limb division.
+
+Copyright 1991, 1993, 1994, 1996, 1998, 1999, 2000, 2002, 2003 Free Software
+Foundation, Inc.
+
+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 3 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. If not, see http://www.gnu.org/licenses/. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+#include "longlong.h"
+
+
+/* The size where udiv_qrnnd_preinv should be used rather than udiv_qrnnd,
+ meaning the quotient size where that should happen, the quotient size
+ being how many udiv divisions will be done.
+
+ The default is to use preinv always, CPUs where this doesn't suit have
+ tuned thresholds. Note in particular that preinv should certainly be
+ used if that's the only division available (USE_PREINV_ALWAYS). */
+
+#ifndef DIVREM_1_NORM_THRESHOLD
+#define DIVREM_1_NORM_THRESHOLD 0
+#endif
+#ifndef DIVREM_1_UNNORM_THRESHOLD
+#define DIVREM_1_UNNORM_THRESHOLD 0
+#endif
+
+
+
+/* If the cpu only has multiply-by-inverse division (eg. alpha), then NORM
+ and UNNORM thresholds are 0 and only the inversion code is included.
+
+ If multiply-by-inverse is never viable, then NORM and UNNORM thresholds
+ will be MP_SIZE_T_MAX and only the plain division code is included.
+
+ Otherwise mul-by-inverse is better than plain division above some
+ threshold, and best results are obtained by having code for both present.
+
+ The main reason for separating the norm and unnorm cases is that not all
+ CPUs give zero for "n0 >> GMP_LIMB_BITS" which would arise in the unnorm
+ code used on an already normalized divisor.
+
+ If UDIV_NEEDS_NORMALIZATION is false then plain division uses the same
+ non-shifting code for both the norm and unnorm cases, though with
+ different criteria for skipping a division, and with different thresholds
+ of course. And in fact if inversion is never viable, then that simple
+ non-shifting division would be all that's left.
+
+ The NORM and UNNORM thresholds might not differ much, but if there's
+ going to be separate code for norm and unnorm then it makes sense to have
+ separate thresholds. One thing that's possible is that the
+ mul-by-inverse might be better only for normalized divisors, due to that
+ case not needing variable bit shifts.
+
+ Notice that the thresholds are tested after the decision to possibly skip
+ one divide step, so they're based on the actual number of divisions done.
+
+ For the unnorm case, it would be possible to call mpn_lshift to adjust
+ the dividend all in one go (into the quotient space say), rather than
+ limb-by-limb in the loop. This might help if mpn_lshift is a lot faster
+ than what the compiler can generate for EXTRACT. But this is left to CPU
+ specific implementations to consider, especially since EXTRACT isn't on
+ the dependent chain. */
+
+mp_limb_t
+mpn_divrem_1 (mp_ptr qp, mp_size_t qxn,
+ mp_srcptr up, mp_size_t un, mp_limb_t d)
+{
+ mp_size_t n;
+ mp_size_t i;
+ mp_limb_t n1, n0;
+ mp_limb_t r = 0;
+
+ ASSERT (qxn >= 0);
+ ASSERT (un >= 0);
+ ASSERT (d != 0);
+ /* FIXME: What's the correct overlap rule when qxn!=0? */
+ ASSERT (MPN_SAME_OR_SEPARATE_P (qp+qxn, up, un));
+
+ n = un + qxn;
+ if (n == 0)
+ return 0;
+
+ d <<= GMP_NAIL_BITS;
+
+ qp += (n - 1); /* Make qp point at most significant quotient limb */
+
+ if ((d & GMP_LIMB_HIGHBIT) != 0)
+ {
+ if (un != 0)
+ {
+ /* High quotient limb is 0 or 1, skip a divide step. */
+ mp_limb_t q;
+ r = up[un - 1] << GMP_NAIL_BITS;
+ q = (r >= d);
+ *qp-- = q;
+ r -= (d & -q);
+ r >>= GMP_NAIL_BITS;
+ n--;
+ un--;
+ }
+
+ if (BELOW_THRESHOLD (n, DIVREM_1_NORM_THRESHOLD))
+ {
+ plain:
+ for (i = un - 1; i >= 0; i--)
+ {
+ n0 = up[i] << GMP_NAIL_BITS;
+ udiv_qrnnd (*qp, r, r, n0, d);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ }
+ for (i = qxn - 1; i >= 0; i--)
+ {
+ udiv_qrnnd (*qp, r, r, CNST_LIMB(0), d);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ }
+ return r;
+ }
+ else
+ {
+ /* Multiply-by-inverse, divisor already normalized. */
+ mp_limb_t dinv;
+ invert_limb (dinv, d);
+
+ for (i = un - 1; i >= 0; i--)
+ {
+ n0 = up[i] << GMP_NAIL_BITS;
+ udiv_qrnnd_preinv (*qp, r, r, n0, d, dinv);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ }
+ for (i = qxn - 1; i >= 0; i--)
+ {
+ udiv_qrnnd_preinv (*qp, r, r, CNST_LIMB(0), d, dinv);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ }
+ return r;
+ }
+ }
+ else
+ {
+ /* Most significant bit of divisor == 0. */
+ int norm;
+
+ /* Skip a division if high < divisor (high quotient 0). Testing here
+ before normalizing will still skip as often as possible. */
+ if (un != 0)
+ {
+ n1 = up[un - 1] << GMP_NAIL_BITS;
+ if (n1 < d)
+ {
+ r = n1 >> GMP_NAIL_BITS;
+ *qp-- = 0;
+ n--;
+ if (n == 0)
+ return r;
+ un--;
+ }
+ }
+
+ if (! UDIV_NEEDS_NORMALIZATION
+ && BELOW_THRESHOLD (n, DIVREM_1_UNNORM_THRESHOLD))
+ goto plain;
+
+ count_leading_zeros (norm, d);
+ d <<= norm;
+ r <<= norm;
+
+ if (UDIV_NEEDS_NORMALIZATION
+ && BELOW_THRESHOLD (n, DIVREM_1_UNNORM_THRESHOLD))
+ {
+ if (un != 0)
+ {
+ n1 = up[un - 1] << GMP_NAIL_BITS;
+ r |= (n1 >> (GMP_LIMB_BITS - norm));
+ for (i = un - 2; i >= 0; i--)
+ {
+ n0 = up[i] << GMP_NAIL_BITS;
+ udiv_qrnnd (*qp, r, r,
+ (n1 << norm) | (n0 >> (GMP_NUMB_BITS - norm)),
+ d);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ n1 = n0;
+ }
+ udiv_qrnnd (*qp, r, r, n1 << norm, d);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ }
+ for (i = qxn - 1; i >= 0; i--)
+ {
+ udiv_qrnnd (*qp, r, r, CNST_LIMB(0), d);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ }
+ return r >> norm;
+ }
+ else
+ {
+ mp_limb_t dinv;
+ invert_limb (dinv, d);
+ if (un != 0)
+ {
+ n1 = up[un - 1] << GMP_NAIL_BITS;
+ r |= (n1 >> (GMP_LIMB_BITS - norm));
+ for (i = un - 2; i >= 0; i--)
+ {
+ n0 = up[i] << GMP_NAIL_BITS;
+ udiv_qrnnd_preinv (*qp, r, r,
+ ((n1 << norm) | (n0 >> (GMP_NUMB_BITS - norm))),
+ d, dinv);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ n1 = n0;
+ }
+ udiv_qrnnd_preinv (*qp, r, r, n1 << norm, d, dinv);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ }
+ for (i = qxn - 1; i >= 0; i--)
+ {
+ udiv_qrnnd_preinv (*qp, r, r, CNST_LIMB(0), d, dinv);
+ r >>= GMP_NAIL_BITS;
+ qp--;
+ }
+ return r >> norm;
+ }
+ }
+}
projects / msp430-gcc.git / blobdiff