source/libs/gmp/gmp-src/mpn/generic/div_qr_1.c

   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 }