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Annotation of OpenXM_contrib/gmp/mpn/generic/gcd_1.c, Revision 1.1

1.1     ! maekawa     1: /* mpn_gcd_1 --
        !             2:
        !             3: Copyright (C) 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: #include "longlong.h"
        !            25:
        !            26: /* Does not work for U == 0 or V == 0.  It would be tough to make it work for
        !            27:    V == 0 since gcd(x,0) = x, and U does not generally fit in an mp_limb_t.  */
        !            28:
        !            29: mp_limb_t
        !            30: mpn_gcd_1 (up, size, vlimb)
        !            31:      mp_srcptr up;
        !            32:      mp_size_t size;
        !            33:      mp_limb_t vlimb;
        !            34: {
        !            35:   mp_limb_t ulimb;
        !            36:   unsigned long int u_low_zero_bits, v_low_zero_bits;
        !            37:
        !            38:   if (size > 1)
        !            39:     {
        !            40:       ulimb = mpn_mod_1 (up, size, vlimb);
        !            41:       if (ulimb == 0)
        !            42:        return vlimb;
        !            43:     }
        !            44:   else
        !            45:     ulimb = up[0];
        !            46:
        !            47:   /*  Need to eliminate low zero bits.  */
        !            48:   count_trailing_zeros (u_low_zero_bits, ulimb);
        !            49:   ulimb >>= u_low_zero_bits;
        !            50:
        !            51:   count_trailing_zeros (v_low_zero_bits, vlimb);
        !            52:   vlimb >>= v_low_zero_bits;
        !            53:
        !            54:   while (ulimb != vlimb)
        !            55:     {
        !            56:       if (ulimb > vlimb)
        !            57:        {
        !            58:          ulimb -= vlimb;
        !            59:          do
        !            60:            ulimb >>= 1;
        !            61:          while ((ulimb & 1) == 0);
        !            62:        }
        !            63:       else /*  vlimb > ulimb.  */
        !            64:        {
        !            65:          vlimb -= ulimb;
        !            66:          do
        !            67:            vlimb >>= 1;
        !            68:          while ((vlimb & 1) == 0);
        !            69:        }
        !            70:     }
        !            71:
        !            72:   return  ulimb << MIN (u_low_zero_bits, v_low_zero_bits);
        !            73: }