github.com/aergoio/aergo@v1.3.1/libtool/src/gmp-6.1.2/mpn/generic/div_qr_1.c (about)

     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.h"
    35  #include "gmp-impl.h"
    36  #include "longlong.h"
    37  
    38  #ifndef DIV_QR_1_NORM_THRESHOLD
    39  #define DIV_QR_1_NORM_THRESHOLD 3
    40  #endif
    41  #ifndef DIV_QR_1_UNNORM_THRESHOLD
    42  #define DIV_QR_1_UNNORM_THRESHOLD 3
    43  #endif
    44  
    45  #if GMP_NAIL_BITS > 0
    46  #error Nail bits not supported
    47  #endif
    48  
    49  /* Divides {up, n} by d. Writes the n-1 low quotient limbs at {qp,
    50   * n-1}, and the high quote limb at *qh. Returns remainder. */
    51  mp_limb_t
    52  mpn_div_qr_1 (mp_ptr qp, mp_limb_t *qh, mp_srcptr up, mp_size_t n,
    53  	      mp_limb_t d)
    54  {
    55    unsigned cnt;
    56    mp_limb_t uh;
    57  
    58    ASSERT (n > 0);
    59    ASSERT (d > 0);
    60  
    61    if (d & GMP_NUMB_HIGHBIT)
    62      {
    63        /* Normalized case */
    64        mp_limb_t dinv, q;
    65  
    66        uh = up[--n];
    67  
    68        q = (uh >= d);
    69        *qh = q;
    70        uh -= (-q) & d;
    71  
    72        if (BELOW_THRESHOLD (n, DIV_QR_1_NORM_THRESHOLD))
    73  	{
    74  	  cnt = 0;
    75  	plain:
    76  	  while (n > 0)
    77  	    {
    78  	      mp_limb_t ul = up[--n];
    79  	      udiv_qrnnd (qp[n], uh, uh, ul, d);
    80  	    }
    81  	  return uh >> cnt;
    82  	}
    83        invert_limb (dinv, d);
    84        return mpn_div_qr_1n_pi1 (qp, up, n, uh, d, dinv);
    85      }
    86    else
    87      {
    88        /* Unnormalized case */
    89        mp_limb_t dinv, ul;
    90  
    91        if (! UDIV_NEEDS_NORMALIZATION
    92  	  && BELOW_THRESHOLD (n, DIV_QR_1_UNNORM_THRESHOLD))
    93  	{
    94  	  uh = up[--n];
    95  	  udiv_qrnnd (*qh, uh, CNST_LIMB(0), uh, d);
    96  	  cnt = 0;
    97  	  goto plain;
    98  	}
    99  
   100        count_leading_zeros (cnt, d);
   101        d <<= cnt;
   102  
   103  #if HAVE_NATIVE_div_qr_1u_pi1
   104        /* FIXME: Call loop doing on-the-fly normalization */
   105  #endif
   106  
   107        /* Shift up front, use qp area for shifted copy. A bit messy,
   108  	 since we have only n-1 limbs available, and shift the high
   109  	 limb manually. */
   110        uh = up[--n];
   111        ul = (uh << cnt) | mpn_lshift (qp, up, n, cnt);
   112        uh >>= (GMP_LIMB_BITS - cnt);
   113  
   114        if (UDIV_NEEDS_NORMALIZATION
   115  	  && BELOW_THRESHOLD (n, DIV_QR_1_UNNORM_THRESHOLD))
   116  	{
   117  	  udiv_qrnnd (*qh, uh, uh, ul, d);
   118  	  up = qp;
   119  	  goto plain;
   120  	}
   121        invert_limb (dinv, d);
   122  
   123        udiv_qrnnd_preinv (*qh, uh, uh, ul, d, dinv);
   124        return mpn_div_qr_1n_pi1 (qp, qp, n, uh, d, dinv) >> cnt;
   125      }
   126  }