libchill/ffsetclrps.c

   1 /* Implement POWERSET runtime actions for CHILL.
   2    Copyright (C) 1992,1993 Free Software Foundation, Inc.
   3    Author: Wilfried Moser, et al
   4
   5 This file is part of GNU CC.
   6
   7 GNU CC is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU CC is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU CC; see the file COPYING.  If not, write to
  19 the Free Software Foundation, 59 Temple Place - Suite 330,
  20 Boston, MA 02111-1307, USA.  */
  21
  22 /* As a special exception, if you link this library with other files,
  23    some of which are compiled with GCC, to produce an executable,
  24    this library does not by itself cause the resulting executable
  25    to be covered by the GNU General Public License.
  26    This exception does not however invalidate any other reasons why
  27    the executable file might be covered by the GNU General Public License.  */
  28
  29 #define __CHILL_LIB__
  30
  31 #include <stdio.h>
  32 #include "powerset.h"
  33
  34 /*
  35  * function __ffsetclrpowerset
  36  *
  37  * parameters:
  38  *      ps              powerset
  39  *      bitlength       length of powerset
  40  *
  41  * returns:
  42  *      int             -1 .. nothing found
  43  *                      >=0 .. index of first true bit found
  44  * exceptions:
  45  *  none
  46  */
  47
  48 int
  49 __ffsetclrpowerset (ps, bitlength, first_bit)
  50      SET_WORD      *ps;
  51      unsigned long  bitlength;
  52      int first_bit;
  53 {
  54   register int bitno;
  55
  56   if (first_bit >= bitlength)
  57     return -1;
  58
  59     {
  60       unsigned int words_to_skip = (unsigned) first_bit / SET_WORD_SIZE;
  61       unsigned long cnt = words_to_skip * SET_WORD_SIZE;
  62       SET_WORD  *p = ps + words_to_skip;
  63       SET_WORD  *endp = ps + BITS_TO_WORDS(bitlength);
  64       SET_WORD  c;
  65       first_bit = (unsigned) first_bit % (unsigned) SET_WORD_SIZE;
  66
  67       c = *p++;
  68       if (c)
  69         {
  70           for (bitno = first_bit; bitno < SET_WORD_SIZE; bitno++)
  71             if (GET_BIT_IN_WORD(c, bitno))
  72               goto found;
  73         }
  74       cnt += SET_WORD_SIZE;
  75
  76       while (p < endp)
  77         {
  78           if ((c = *p++))
  79             {
  80               /* found a bit set .. calculate which */
  81               for (bitno = 0; bitno < SET_WORD_SIZE; bitno++)
  82                 if (GET_BIT_IN_WORD(c, bitno))
  83                   goto found;
  84             }
  85           cnt += SET_WORD_SIZE;
  86         }
  87       return -1;
  88     found:
  89       bitno += cnt;
  90       return bitno >= bitlength ? -1 : bitno;
  91     }
  92 }