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Annotation of OpenXM_contrib/gmp/mpn/generic/scan0.c, Revision 1.1.1.3

1.1       maekawa     1: /* mpn_scan0 -- Scan from a given bit position for the next clear bit.
                      2:
1.1.1.3 ! ohara       3: Copyright 1994, 1996, 2001, 2002 Free Software Foundation, Inc.
1.1       maekawa     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
1.1.1.2   maekawa     8: it under the terms of the GNU Lesser General Public License as published by
                      9: the Free Software Foundation; either version 2.1 of the License, or (at your
1.1       maekawa    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
1.1.1.2   maekawa    14: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
1.1       maekawa    15: License for more details.
                     16:
1.1.1.2   maekawa    17: You should have received a copy of the GNU Lesser General Public License
1.1       maekawa    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: /* Design issues:
                     27:    1. What if starting_bit is not within U?  Caller's problem?
                     28:    2. Bit index should be 'unsigned'?
                     29:
                     30:    Argument constraints:
1.1.1.3 ! ohara      31:    1. U must sooner or later have a limb with a clear bit.
1.1       maekawa    32:  */
                     33:
                     34: unsigned long int
                     35: mpn_scan0 (register mp_srcptr up,
                     36:           register unsigned long int starting_bit)
                     37: {
                     38:   mp_size_t starting_word;
                     39:   mp_limb_t alimb;
                     40:   int cnt;
                     41:   mp_srcptr p;
                     42:
                     43:   /* Start at the word implied by STARTING_BIT.  */
1.1.1.3 ! ohara      44:   starting_word = starting_bit / GMP_NUMB_BITS;
1.1       maekawa    45:   p = up + starting_word;
1.1.1.3 ! ohara      46:   alimb = *p++ ^ GMP_NUMB_MASK;
1.1       maekawa    47:
                     48:   /* Mask off any bits before STARTING_BIT in the first limb.  */
1.1.1.3 ! ohara      49:   alimb &= - (mp_limb_t) 1 << (starting_bit % GMP_NUMB_BITS);
1.1       maekawa    50:
                     51:   while (alimb == 0)
1.1.1.3 ! ohara      52:     alimb = *p++ ^ GMP_NUMB_MASK;
1.1       maekawa    53:
1.1.1.3 ! ohara      54:   count_trailing_zeros (cnt, alimb);
        !            55:   return (p - up - 1) * GMP_NUMB_BITS + cnt;
1.1       maekawa    56: }