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Annotation of OpenXM_contrib/gmp/mpn/generic/gcd_1.c, Revision 1.1.1.1

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: }