redc_2.c revision 1.1.1.1 
1/* mpn_redc_2.  Set cp[] <- up[]/R^n mod mp[].  Clobber up[].
2   mp[] is n limbs; up[] is 2n limbs.
3
4   THIS IS AN INTERNAL FUNCTION WITH A MUTABLE INTERFACE.  IT IS ONLY
5   SAFE TO REACH THIS FUNCTION THROUGH DOCUMENTED INTERFACES.
6
7Copyright (C) 2000, 2001, 2002, 2004, 2008 Free Software Foundation, Inc.
8
9This file is part of the GNU MP Library.
10
11The GNU MP Library is free software; you can redistribute it and/or modify
12it under the terms of the GNU Lesser General Public License as published by
13the Free Software Foundation; either version 3 of the License, or (at your
14option) any later version.
15
16The GNU MP Library is distributed in the hope that it will be useful, but
17WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
18or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
19License for more details.
20
21You should have received a copy of the GNU Lesser General Public License
22along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
23
24#include "gmp.h"
25#include "gmp-impl.h"
26#include "longlong.h"
27
28
29#if GMP_NAIL_BITS != 0
30you lose
31#endif
32
33/* For testing purposes, define our own mpn_addmul_2 if there is none already
34   available.  */
35#ifndef HAVE_NATIVE_mpn_addmul_2
36mp_limb_t
37mpn_addmul_2 (mp_ptr rp, mp_srcptr up, mp_size_t n, mp_srcptr vp)
38{
39  rp[n] = mpn_addmul_1 (rp, up, n, vp[0]);
40  return mpn_addmul_1 (rp + 1, up, n, vp[1]);
41}
42#endif
43
44#if defined (__GNUC__) && defined (__ia64) && W_TYPE_SIZE == 64
45#define umul2low(ph, pl, uh, ul, vh, vl) \
46  do {									\
47    mp_limb_t _ph, _pl;							\
48    __asm__ ("xma.hu %0 = %3, %5, f0\n\t"				\
49	     "xma.l %1 = %3, %5, f0\n\t"				\
50	     ";;\n\t"							\
51	     "xma.l %0 = %3, %4, %0\n\t"				\
52	     ";;\n\t"							\
53	     "xma.l %0 = %2, %5, %0"					\
54	     : "=&f" (ph), "=&f" (pl)					\
55	     : "f" (uh), "f" (ul), "f" (vh), "f" (vl));			\
56  } while (0)
57#endif
58
59#ifndef umul2low
60#define umul2low(ph, pl, uh, ul, vh, vl) \
61  do {									\
62    mp_limb_t _ph, _pl;							\
63    umul_ppmm (_ph, _pl, ul, vl);					\
64    (ph) = _ph + (ul) * (vh) + (uh) * (vl);				\
65    (pl) = _pl;								\
66  } while (0)
67#endif
68
69void
70mpn_redc_2 (mp_ptr rp, mp_ptr up, mp_srcptr mp, mp_size_t n, mp_srcptr mip)
71{
72  mp_limb_t q[2];
73  mp_size_t j;
74  mp_limb_t upn;
75  mp_limb_t cy;
76
77  ASSERT (n > 0);
78  ASSERT_MPN (up, 2*n);
79
80  if ((n & 1) != 0)
81    {
82      up[0] = mpn_addmul_1 (up, mp, n, (up[0] * mip[0]) & GMP_NUMB_MASK);
83      up++;
84    }
85
86  for (j = n - 2; j >= 0; j -= 2)
87    {
88      umul2low (q[1], q[0], mip[1], mip[0], up[1], up[0]);
89      upn = up[n];		/* mpn_addmul_2 overwrites this */
90      up[1] = mpn_addmul_2 (up, mp, n, q);
91      up[0] = up[n];
92      up[n] = upn;
93      up += 2;
94    }
95  cy = mpn_add_n (rp, up, up - n, n);
96  if (cy != 0)
97    mpn_sub_n (rp, rp, mp, n);
98}
99