libchill/flsetclrps.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, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  20
  21 #define __CHILL_LIB__
  22
  23 #include <stdio.h>
  24 #include "powerset.h"
  25
  26 /*
  27  * function __flsetclrpowerset
  28  *
  29  * parameters:
  30  *      ps              powerset
  31  *      bitlength       length of powerset
  32  *
  33  * returns:
  34  *      int             -1 .. nothing found
  35  *                      >= 0 .. index of last set bit
  36  * exceptions:
  37  *  none
  38  *
  39  * abstract:
  40  *  Find last bit set in a powerset and return the corresponding value
  41  *  in *out and clear this bit. Return 0 for no more found, else 1.
  42  *
  43  */
  44 int
  45 __flsetclrpowerset (ps, bitlength, first_bit)
  46      SET_WORD      *ps;
  47      unsigned long  bitlength;
  48      int first_bit;
  49 {
  50   register int bitno;
  51
  52 #ifndef USE_CHARS
  53   if (bitlength <= SET_CHAR_SIZE)
  54     {
  55       for (bitno = bitlength - 1; bitno >= first_bit; bitno--)
  56         if (GET_BIT_IN_CHAR (*((SET_CHAR *)ps), bitno))
  57           break;
  58       return bitno < first_bit ? -1 : bitno;
  59     }
  60   else if (bitlength <= SET_SHORT_SIZE)
  61     {
  62       for (bitno = bitlength - 1; bitno >= first_bit; bitno--)
  63         if (GET_BIT_IN_SHORT (*((SET_SHORT *)ps), bitno))
  64           break;
  65       return bitno < first_bit ? -1 : bitno;
  66     }
  67   else
  68 #endif
  69     {
  70       SET_WORD *p, c;
  71       bitno = bitlength - 1;
  72       if (bitno < first_bit)
  73         return -1;
  74       p = &ps[(unsigned) bitno / SET_WORD_SIZE];
  75       c = *p;
  76       if (((unsigned) bitlength % SET_WORD_SIZE) != 0)
  77         MASK_UNUSED_WORD_BITS(&c, (unsigned) bitlength % SET_WORD_SIZE);
  78       if (c)
  79         goto found;
  80       else
  81         bitno -= ((unsigned) bitno % SET_WORD_SIZE) + 1;
  82       while (bitno >= first_bit)
  83         {
  84           c = *--p;
  85           if (c)
  86             goto found;
  87           bitno -= SET_WORD_SIZE;
  88         }
  89       return -1;
  90     found:
  91       for (; bitno >= first_bit; bitno--)
  92         {
  93           if (GET_BIT_IN_WORD (c, (unsigned) bitno % SET_WORD_SIZE))
  94             return bitno;
  95         }
  96       return -1;
  97     }
  98 }