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Annotation of OpenXM_contrib/gmp/mpn/generic/rshift.c, Revision 1.1

1.1     ! maekawa     1: /* mpn_rshift -- Shift right a low-level natural-number integer.
        !             2:
        !             3: Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
        !             4:
        !             5: This file is part of the GNU MP Library.
        !             6:
        !             7: The GNU MP Library is free software; you can redistribute it and/or modify
        !             8: it under the terms of the GNU Library General Public License as published by
        !             9: the Free Software Foundation; either version 2 of the License, or (at your
        !            10: option) any later version.
        !            11:
        !            12: The GNU MP Library is distributed in the hope that it will be useful, but
        !            13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
        !            15: License for more details.
        !            16:
        !            17: You should have received a copy of the GNU Library General Public License
        !            18: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
        !            19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            20: MA 02111-1307, USA. */
        !            21:
        !            22: #include "gmp.h"
        !            23: #include "gmp-impl.h"
        !            24:
        !            25: /* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
        !            26:    and store the USIZE least significant limbs of the result at WP.
        !            27:    The bits shifted out to the right are returned.
        !            28:
        !            29:    Argument constraints:
        !            30:    1. 0 < CNT < BITS_PER_MP_LIMB
        !            31:    2. If the result is to be written over the input, WP must be <= UP.
        !            32: */
        !            33:
        !            34: mp_limb_t
        !            35: #if __STDC__
        !            36: mpn_rshift (register mp_ptr wp,
        !            37:            register mp_srcptr up, mp_size_t usize,
        !            38:            register unsigned int cnt)
        !            39: #else
        !            40: mpn_rshift (wp, up, usize, cnt)
        !            41:      register mp_ptr wp;
        !            42:      register mp_srcptr up;
        !            43:      mp_size_t usize;
        !            44:      register unsigned int cnt;
        !            45: #endif
        !            46: {
        !            47:   register mp_limb_t high_limb, low_limb;
        !            48:   register unsigned sh_1, sh_2;
        !            49:   register mp_size_t i;
        !            50:   mp_limb_t retval;
        !            51:
        !            52: #ifdef DEBUG
        !            53:   if (usize == 0 || cnt == 0)
        !            54:     abort ();
        !            55: #endif
        !            56:
        !            57:   sh_1 = cnt;
        !            58:
        !            59: #if 0
        !            60:   if (sh_1 == 0)
        !            61:     {
        !            62:       if (wp != up)
        !            63:        {
        !            64:          /* Copy from low end to high end, to allow specified input/output
        !            65:             overlapping.  */
        !            66:          for (i = 0; i < usize; i++)
        !            67:            wp[i] = up[i];
        !            68:        }
        !            69:       return usize;
        !            70:     }
        !            71: #endif
        !            72:
        !            73:   wp -= 1;
        !            74:   sh_2 = BITS_PER_MP_LIMB - sh_1;
        !            75:   high_limb = up[0];
        !            76:   retval = high_limb << sh_2;
        !            77:   low_limb = high_limb;
        !            78:
        !            79:   for (i = 1; i < usize; i++)
        !            80:     {
        !            81:       high_limb = up[i];
        !            82:       wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
        !            83:       low_limb = high_limb;
        !            84:     }
        !            85:   wp[i] = low_limb >> sh_1;
        !            86:
        !            87:   return retval;
        !            88: }