1  /* mpn_div_qr_1 -- mpn by limb division.
       2  
       3     Contributed to the GNU project by Niels Möller and Torbjörn Granlund
       4  
       5  Copyright 1991, 1993, 1994, 1996, 1998-2000, 2002, 2003, 2013 Free Software
       6  Foundation, Inc.
       7  
       8  This file is part of the GNU MP Library.
       9  
      10  The GNU MP Library is free software; you can redistribute it and/or modify
      11  it under the terms of either:
      12  
      13    * the GNU Lesser General Public License as published by the Free
      14      Software Foundation; either version 3 of the License, or (at your
      15      option) any later version.
      16  
      17  or
      18  
      19    * the GNU General Public License as published by the Free Software
      20      Foundation; either version 2 of the License, or (at your option) any
      21      later version.
      22  
      23  or both in parallel, as here.
      24  
      25  The GNU MP Library is distributed in the hope that it will be useful, but
      26  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
      27  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
      28  for more details.
      29  
      30  You should have received copies of the GNU General Public License and the
      31  GNU Lesser General Public License along with the GNU MP Library.  If not,
      32  see https://www.gnu.org/licenses/.  */
      33  
      34  #include "gmp-impl.h"
      35  #include "longlong.h"
      36  
      37  #ifndef DIV_QR_1_NORM_THRESHOLD
      38  #define DIV_QR_1_NORM_THRESHOLD 3
      39  #endif
      40  #ifndef DIV_QR_1_UNNORM_THRESHOLD
      41  #define DIV_QR_1_UNNORM_THRESHOLD 3
      42  #endif
      43  
      44  #if GMP_NAIL_BITS > 0
      45  #error Nail bits not supported
      46  #endif
      47  
      48  /* Divides {up, n} by d. Writes the n-1 low quotient limbs at {qp,
      49   * n-1}, and the high quotient limb at *qh. Returns remainder. */
      50  mp_limb_t
      51  mpn_div_qr_1 (mp_ptr qp, mp_limb_t *qh, mp_srcptr up, mp_size_t n,
      52  	      mp_limb_t d)
      53  {
      54    unsigned cnt;
      55    mp_limb_t uh;
      56  
      57    ASSERT (n > 0);
      58    ASSERT (d > 0);
      59  
      60    if (d & GMP_NUMB_HIGHBIT)
      61      {
      62        /* Normalized case */
      63        mp_limb_t dinv, q;
      64  
      65        uh = up[--n];
      66  
      67        q = (uh >= d);
      68        *qh = q;
      69        uh -= (-q) & d;
      70  
      71        if (BELOW_THRESHOLD (n, DIV_QR_1_NORM_THRESHOLD))
      72  	{
      73  	  cnt = 0;
      74  	plain:
      75  	  while (n > 0)
      76  	    {
      77  	      mp_limb_t ul = up[--n];
      78  	      udiv_qrnnd (qp[n], uh, uh, ul, d);
      79  	    }
      80  	  return uh >> cnt;
      81  	}
      82        invert_limb (dinv, d);
      83        return mpn_div_qr_1n_pi1 (qp, up, n, uh, d, dinv);
      84      }
      85    else
      86      {
      87        /* Unnormalized case */
      88        mp_limb_t dinv, ul;
      89  
      90        if (! UDIV_NEEDS_NORMALIZATION
      91  	  && BELOW_THRESHOLD (n, DIV_QR_1_UNNORM_THRESHOLD))
      92  	{
      93  	  uh = up[--n];
      94  	  udiv_qrnnd (*qh, uh, CNST_LIMB(0), uh, d);
      95  	  cnt = 0;
      96  	  goto plain;
      97  	}
      98  
      99        count_leading_zeros (cnt, d);
     100        d <<= cnt;
     101  
     102  #if HAVE_NATIVE_mpn_div_qr_1u_pi1
     103        /* FIXME: Call loop doing on-the-fly normalization */
     104  #endif
     105  
     106        /* Shift up front, use qp area for shifted copy. A bit messy,
     107  	 since we have only n-1 limbs available, and shift the high
     108  	 limb manually. */
     109        uh = up[--n];
     110        ul = (uh << cnt) | mpn_lshift (qp, up, n, cnt);
     111        uh >>= (GMP_LIMB_BITS - cnt);
     112  
     113        if (UDIV_NEEDS_NORMALIZATION
     114  	  && BELOW_THRESHOLD (n, DIV_QR_1_UNNORM_THRESHOLD))
     115  	{
     116  	  udiv_qrnnd (*qh, uh, uh, ul, d);
     117  	  up = qp;
     118  	  goto plain;
     119  	}
     120        invert_limb (dinv, d);
     121  
     122        udiv_qrnnd_preinv (*qh, uh, uh, ul, d, dinv);
     123        return mpn_div_qr_1n_pi1 (qp, qp, n, uh, d, dinv) >> cnt;
     124      }
     125  }