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Annotation of OpenXM_contrib/gmp/mpn/generic/scan0.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpn_scan0 -- Scan from a given bit position for the next clear bit.
                      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: /* 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:
                     31:    1. U must sooner ot later have a limb with a clear bit.
                     32:  */
                     33:
                     34: unsigned long int
                     35: #if __STDC__
                     36: mpn_scan0 (register mp_srcptr up,
                     37:           register unsigned long int starting_bit)
                     38: #else
                     39: mpn_scan0 (up, starting_bit)
                     40:      register mp_srcptr up;
                     41:      register unsigned long int starting_bit;
                     42: #endif
                     43: {
                     44:   mp_size_t starting_word;
                     45:   mp_limb_t alimb;
                     46:   int cnt;
                     47:   mp_srcptr p;
                     48:
                     49:   /* Start at the word implied by STARTING_BIT.  */
                     50:   starting_word = starting_bit / BITS_PER_MP_LIMB;
                     51:   p = up + starting_word;
                     52:   alimb = ~*p++;
                     53:
                     54:   /* Mask off any bits before STARTING_BIT in the first limb.  */
                     55:   alimb &= - (mp_limb_t) 1 << (starting_bit % BITS_PER_MP_LIMB);
                     56:
                     57:   while (alimb == 0)
                     58:     alimb = ~*p++;
                     59:
                     60:   count_leading_zeros (cnt, alimb & -alimb);
                     61:   return (p - up) * BITS_PER_MP_LIMB - 1 - cnt;
                     62: }