2005-12-13 Ulrich Drepper <drepper@redhat.com>

1 files changed, 245 insertions, 0 deletions

diff --git a/stdlib/divrem.c b/stdlib/divrem.c
new file mode 100644
index 0000000..c97d01e
--- /dev/null
+++ b/stdlib/divrem.c
@@ -0,0 +1,245 @@
+/* mpn_divrem -- Divide natural numbers, producing both remainder and
+   quotient.
+
+Copyright (C) 1993, 1994, 1995, 1996 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 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"
+#include "longlong.h"
+
+/* Divide num (NP/NSIZE) by den (DP/DSIZE) and write
+   the NSIZE-DSIZE least significant quotient limbs at QP
+   and the DSIZE long remainder at NP.  If QEXTRA_LIMBS is
+   non-zero, generate that many fraction bits and append them after the
+   other quotient limbs.
+   Return the most significant limb of the quotient, this is always 0 or 1.
+
+   Preconditions:
+   0. NSIZE >= DSIZE.
+   1. The most significant bit of the divisor must be set.
+   2. QP must either not overlap with the input operands at all, or
+      QP + DSIZE >= NP must hold true.  (This means that it's
+      possible to put the quotient in the high part of NUM, right after the
+      remainder in NUM.
+   3. NSIZE >= DSIZE, even if QEXTRA_LIMBS is non-zero.  */
+
+mp_limb_t
+#if __STDC__
+mpn_divrem (mp_ptr qp, mp_size_t qextra_limbs,
+	    mp_ptr np, mp_size_t nsize,
+	    mp_srcptr dp, mp_size_t dsize)
+#else
+mpn_divrem (qp, qextra_limbs, np, nsize, dp, dsize)
+     mp_ptr qp;
+     mp_size_t qextra_limbs;
+     mp_ptr np;
+     mp_size_t nsize;
+     mp_srcptr dp;
+     mp_size_t dsize;
+#endif
+{
+  mp_limb_t most_significant_q_limb = 0;
+
+  switch (dsize)
+    {
+    case 0:
+      /* We are asked to divide by zero, so go ahead and do it!  (To make
+	 the compiler not remove this statement, return the value.)  */
+      return 1 / dsize;
+
+    case 1:
+      {
+	mp_size_t i;
+	mp_limb_t n1;
+	mp_limb_t d;
+
+	d = dp[0];
+	n1 = np[nsize - 1];
+
+	if (n1 >= d)
+	  {
+	    n1 -= d;
+	    most_significant_q_limb = 1;
+	  }
+
+	qp += qextra_limbs;
+	for (i = nsize - 2; i >= 0; i--)
+	  udiv_qrnnd (qp[i], n1, n1, np[i], d);
+	qp -= qextra_limbs;
+
+	for (i = qextra_limbs - 1; i >= 0; i--)
+	  udiv_qrnnd (qp[i], n1, n1, 0, d);
+
+	np[0] = n1;
+      }
+      break;
+
+    case 2:
+      {
+	mp_size_t i;
+	mp_limb_t n1, n0, n2;
+	mp_limb_t d1, d0;
+
+	np += nsize - 2;
+	d1 = dp[1];
+	d0 = dp[0];
+	n1 = np[1];
+	n0 = np[0];
+
+	if (n1 >= d1 && (n1 > d1 || n0 >= d0))
+	  {
+	    sub_ddmmss (n1, n0, n1, n0, d1, d0);
+	    most_significant_q_limb = 1;
+	  }
+
+	for (i = qextra_limbs + nsize - 2 - 1; i >= 0; i--)
+	  {
+	    mp_limb_t q;
+	    mp_limb_t r;
+
+	    if (i >= qextra_limbs)
+	      np--;
+	    else
+	      np[0] = 0;
+
+	    if (n1 == d1)
+	      {
+		/* Q should be either 111..111 or 111..110.  Need special
+		   treatment of this rare case as normal division would
+		   give overflow.  */
+		q = ~(mp_limb_t) 0;
+
+		r = n0 + d1;
+		if (r < d1)	/* Carry in the addition? */
+		  {
+		    add_ssaaaa (n1, n0, r - d0, np[0], 0, d0);
+		    qp[i] = q;
+		    continue;
+		  }
+		n1 = d0 - (d0 != 0);
+		n0 = -d0;
+	      }
+	    else
+	      {
+		udiv_qrnnd (q, r, n1, n0, d1);
+		umul_ppmm (n1, n0, d0, q);
+	      }
+
+	    n2 = np[0];
+	  q_test:
+	    if (n1 > r || (n1 == r && n0 > n2))
+	      {
+		/* The estimated Q was too large.  */
+		q--;
+
+		sub_ddmmss (n1, n0, n1, n0, 0, d0);
+		r += d1;
+		if (r >= d1)	/* If not carry, test Q again.  */
+		  goto q_test;
+	      }
+
+	    qp[i] = q;
+	    sub_ddmmss (n1, n0, r, n2, n1, n0);
+	  }
+	np[1] = n1;
+	np[0] = n0;
+      }
+      break;
+
+    default:
+      {
+	mp_size_t i;
+	mp_limb_t dX, d1, n0;
+
+	np += nsize - dsize;
+	dX = dp[dsize - 1];
+	d1 = dp[dsize - 2];
+	n0 = np[dsize - 1];
+
+	if (n0 >= dX)
+	  {
+	    if (n0 > dX || mpn_cmp (np, dp, dsize - 1) >= 0)
+	      {
+		mpn_sub_n (np, np, dp, dsize);
+		n0 = np[dsize - 1];
+		most_significant_q_limb = 1;
+	      }
+	  }
+
+	for (i = qextra_limbs + nsize - dsize - 1; i >= 0; i--)
+	  {
+	    mp_limb_t q;
+	    mp_limb_t n1, n2;
+	    mp_limb_t cy_limb;
+
+	    if (i >= qextra_limbs)
+	      {
+		np--;
+		n2 = np[dsize];
+	      }
+	    else
+	      {
+		n2 = np[dsize - 1];
+		MPN_COPY_DECR (np + 1, np, dsize);
+		np[0] = 0;
+	      }
+
+	    if (n0 == dX)
+	      /* This might over-estimate q, but it's probably not worth
+		 the extra code here to find out.  */
+	      q = ~(mp_limb_t) 0;
+	    else
+	      {
+		mp_limb_t r;
+
+		udiv_qrnnd (q, r, n0, np[dsize - 1], dX);
+		umul_ppmm (n1, n0, d1, q);
+
+		while (n1 > r || (n1 == r && n0 > np[dsize - 2]))
+		  {
+		    q--;
+		    r += dX;
+		    if (r < dX)	/* I.e. "carry in previous addition?"  */
+		      break;
+		    n1 -= n0 < d1;
+		    n0 -= d1;
+		  }
+	      }
+
+	    /* Possible optimization: We already have (q * n0) and (1 * n1)
+	       after the calculation of q.  Taking advantage of that, we
+	       could make this loop make two iterations less.  */
+
+	    cy_limb = mpn_submul_1 (np, dp, dsize, q);
+
+	    if (n2 != cy_limb)
+	      {
+		mpn_add_n (np, np, dp, dsize);
+		q--;
+	      }
+
+	    qp[i] = q;
+	    n0 = np[dsize - 1];
+	  }
+      }
+    }
+
+  return most_significant_q_limb;
+}