* mpf/div.c: Use mpn_tdiv_qr. Use just one TMP_ALLOC. Use full

	divisor, since truncating can lose accuracy.

1 files changed, 76 insertions, 68 deletions

diff --git a/mpf/div.c b/mpf/div.c
index ce03b60b1..32b39b442 100644
--- a/mpf/div.c
+++ b/mpf/div.c
@@ -1,6 +1,7 @@
 /* mpf_div -- Divide two floats.
 
-Copyright 1993, 1994, 1996, 2000, 2001, 2002 Free Software Foundation, Inc.
+Copyright 1993, 1994, 1996, 2000, 2001, 2002, 2004 Free Software Foundation,
+Inc.
 
 This file is part of the GNU MP Library.
 
@@ -19,21 +20,49 @@ 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 <stdio.h>  /* for NULL */
 #include "gmp.h"
 #include "gmp-impl.h"
 #include "longlong.h"
 
+
+/* Not done:
+
+   No attempt is made to identify an overlap u==v.  The result will be
+   correct (1.0), but a full actual division is done whereas of course
+   x/x==1 needs no work.  Such a call is not a sensible thing to make, and
+   it's left to an application to notice and optimize if it might arise
+   somehow through pointer aliasing or whatever.
+
+   Enhancements:
+
+   The high quotient limb is non-zero when high{up,vsize} >= {vp,vsize}.  We
+   could make that comparison and use qsize==prec instead of qsize==prec+1,
+   to save one limb in the division.
+
+   If r==u but the size is enough bigger than prec that there won't be an
+   overlap between quotient and dividend in mpn_tdiv_qr, then we can avoid
+   copying up,usize.  This would only arise from a prec reduced with
+   mpf_set_prec_raw and will be pretty unusual, but might be worthwhile if
+   it could be worked into the copy_u decision cleanly.
+
+   Future:
+
+   If/when mpn_tdiv_qr supports its qxn parameter we can use that instead of
+   padding u with zeros in temporary space.
+
+   If/when a quotient-only division exists it can be used here immediately.
+   remp is only to satisfy mpn_tdiv_qr, the remainder is not used.  */
+
 void
 mpf_div (mpf_ptr r, mpf_srcptr u, mpf_srcptr v)
 {
   mp_srcptr up, vp;
-  mp_ptr rp, tp, rtp;
-  mp_size_t usize, vsize;
-  mp_size_t rsize, tsize;
-  mp_size_t sign_quotient;
-  mp_size_t prec;
-  mp_limb_t q_limb;
+  mp_ptr rp, remp, tp, new_vp;
+  mp_size_t usize, vsize, rsize, prospective_rsize, tsize, zeros, copy_v_size;
+  mp_size_t sign_quotient, prec, high_zero, chop;
   mp_exp_t rexp;
+  int copy_u;
   TMP_DECL (marker);
 
   usize = u->_mp_size;
@@ -54,86 +83,65 @@ mpf_div (mpf_ptr r, mpf_srcptr u, mpf_srcptr v)
     }
 
   TMP_MARK (marker);
-  rexp = u->_mp_exp - v->_mp_exp;
+  rexp = u->_mp_exp - v->_mp_exp + 1;
 
   rp = r->_mp_d;
   up = u->_mp_d;
   vp = v->_mp_d;
 
-  if (vsize > prec)
-    {
-      vp += vsize - prec;
-      vsize = prec;
-    }
+  prospective_rsize = usize - vsize + 1; /* quot from using given u,v sizes */
+  rsize = prec + 1;                      /* desired quot */
 
-  tsize = vsize + prec;
-  tp = (mp_ptr) TMP_ALLOC ((tsize + 1) * BYTES_PER_MP_LIMB);
+  zeros = rsize - prospective_rsize;     /* padding u to give rsize */
+  copy_u = (zeros > 0 || rp == up);      /* copy u if overlap or padding */
 
-  if (usize > tsize)
+  chop = MAX (-zeros, 0);                /* negative zeros means shorten u */
+  up += chop;
+  usize -= chop;
+  zeros += chop;                         /* now zeros >= 0 */
+
+  tsize = usize + zeros;                 /* size for possible copy of u */
+
+  if (WANT_TMP_DEBUG)
     {
-      up += usize - tsize;
-      usize = tsize;
-      rtp = tp;
+      /* separate blocks, for malloc debugging */
+      remp = TMP_ALLOC_LIMBS (vsize);
+      tp = (copy_u ? TMP_ALLOC_LIMBS (tsize) : NULL);
+      new_vp = (rp == vp ? TMP_ALLOC_LIMBS (vsize) : NULL);
     }
   else
     {
-      MPN_ZERO (tp, tsize - usize);
-      rtp = tp + (tsize - usize);
+      /* one block with conditionalized size, for efficiency */
+      copy_v_size = (rp == vp ? vsize : 0);
+      remp = TMP_ALLOC_LIMBS (vsize + copy_v_size + (copy_u ? tsize : 0));
+      new_vp = remp + vsize;
+      tp = new_vp + copy_v_size;
     }
 
-
-  /* Normalize the divisor and the dividend.  */
-  if ((vp[vsize-1] & GMP_NUMB_HIGHBIT) == 0)
-    {
-      mp_ptr tmp;
-      mp_limb_t nlimb;
-      unsigned normalization_steps;
-
-      count_leading_zeros (normalization_steps, vp[vsize - 1]);
-      normalization_steps -= GMP_NAIL_BITS;
-
-      /* Shift up the divisor setting the most significant bit of
-	 the most significant limb.  Use temporary storage not to clobber
-	 the original contents of the divisor.  */
-      tmp = (mp_ptr) TMP_ALLOC (vsize * BYTES_PER_MP_LIMB);
-      mpn_lshift (tmp, vp, vsize, normalization_steps);
-      vp = tmp;
-
-      /* Shift up the dividend, possibly introducing a new most
-	 significant word.  Move the shifted dividend in the remainder
-	 at the same time.  */
-      nlimb = mpn_lshift (rtp, up, usize, normalization_steps);
-      if (nlimb != 0)
-	{
-	  rtp[usize] = nlimb;
-	  tsize++;
-	  rexp++;
-	}
-    }
-  else
+  /* copy and possibly extend u if necessary */
+  if (copy_u)
     {
-      /* The divisor is already normalized, as required.
-	 Copy it to temporary space if it overlaps with the quotient.  */
-      if (vp - rp <= tsize - vsize)
-	{
-	  mp_ptr tmp = (mp_ptr) TMP_ALLOC (vsize * BYTES_PER_MP_LIMB);
-	  MPN_COPY (tmp, vp, vsize);
-	  vp = (mp_srcptr) tmp;
-	}
-
-      /* Move the dividend to the remainder.  */
-      MPN_COPY (rtp, up, usize);
+      MPN_ZERO (tp, zeros);
+      MPN_COPY (tp+zeros, up, usize);
+      up = tp;
+      usize = tsize;
     }
 
-  q_limb = mpn_divmod (rp, tp, tsize, vp, vsize);
-  rsize = tsize - vsize;
-  if (q_limb)
+  /* ensure divisor doesn't overlap quotient */
+  if (rp == vp)
     {
-      rp[rsize] = q_limb;
-      rsize++;
-      rexp++;
+      MPN_COPY (new_vp, vp, vsize);
+      vp = new_vp;
     }
 
+  ASSERT (usize-vsize+1 == rsize);
+  mpn_tdiv_qr (rp, remp, (mp_size_t) 0, up, usize, vp, vsize);
+
+  /* strip possible zero high limb */
+  high_zero = (rp[rsize-1] == 0);
+  rsize -= high_zero;
+  rexp -= high_zero;
+
   r->_mp_size = sign_quotient >= 0 ? rsize : -rsize;
   r->_mp_exp = rexp;
   TMP_FREE (marker);