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   1 /* -*-c-*-
   2  *
   3  * $Id: mpscan.h,v 1.5 2004/04/08 01:36:15 mdw Exp $
   4  *
   5  * Sequential bit scan of multiprecision integers
   6  *
   7  * (c) 1999 Straylight/Edgeware
   8  */
   9
  10 /*----- Licensing notice --------------------------------------------------*
  11  *
  12  * This file is part of Catacomb.
  13  *
  14  * Catacomb is free software; you can redistribute it and/or modify
  15  * it under the terms of the GNU Library General Public License as
  16  * published by the Free Software Foundation; either version 2 of the
  17  * License, or (at your option) any later version.
  18  *
  19  * Catacomb is distributed in the hope that it will be useful,
  20  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  21  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  22  * GNU Library General Public License for more details.
  23  *
  24  * You should have received a copy of the GNU Library General Public
  25  * License along with Catacomb; if not, write to the Free
  26  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  27  * MA 02111-1307, USA.
  28  */
  29
  30 #ifndef CATACOMB_MPSCAN_H
  31 #define CATACOMB_MPSCAN_H
  32
  33 #ifdef __cplusplus
  34   extern "C" {
  35 #endif
  36
  37 /*----- Header files ------------------------------------------------------*/
  38
  39 #ifndef CATACOMB_MPW_H
  40 #  include "mpw.h"
  41 #endif
  42
  43 /*----- Data structures ---------------------------------------------------*/
  44
  45 typedef struct mpscan {
  46   const mpw *v, *vl;                    /* Vector of words to scan */
  47   mpw w;                                /* Current word to scan */
  48   int bits;                             /* Number of bits left in @w@ */
  49 } mpscan;
  50
  51 /*----- Right-to-left scanning --------------------------------------------*/
  52
  53 /* --- @mpscan_initx@ --- *
  54  *
  55  * Arguments:   @mpscan *m@ = pointer to bitscanner structure
  56  *              @const mpw *v, *vl@ = vector of words to scan
  57  *
  58  * Returns:     ---
  59  *
  60  * Use:         Initializes a bitscanner from a low-level base-and-limit
  61  *              representation of an integer.  Initially no bit is ready; you
  62  *              must call @mpscan_step@ before anything useful will come
  63  *              out.
  64  */
  65
  66 #define MPSCAN_INITX(m_, v_, vl_) do {                                  \
  67   mpscan *_m = (m_);                                                    \
  68   _m->v = (v_);                                                         \
  69   _m->vl = (vl_);                                                       \
  70   _m->bits = 0;                                                         \
  71 } while (0)
  72
  73 extern void mpscan_initx(mpscan */*m*/, const mpw */*v*/, const mpw */*vl*/);
  74
  75 /* --- @mpscan_step@ --- *
  76  *
  77  * Arguments:   @mpscan *m@ = pointer to bitscanner
  78  *
  79  * Returns:     Nonzero if there is another bit to read.
  80  *
  81  * Use:         Steps on to the next bit in the integer.  The macro version
  82  *              evaluates its argument multiple times.
  83  */
  84
  85 #define MPSCAN_STEP(m)                                                  \
  86   ((m)->bits ? ((m)->w >>= 1, (m)->bits--, 1) :                         \
  87    (m)->v < (m)->vl ? ((m)->w = *(m)->v++,                              \
  88                        (m)->bits = MPW_BITS - 1, 1) :                   \
  89    0)
  90
  91 extern int mpscan_step(mpscan */*m*/);
  92
  93 /* --- @mpscan_bit@ --- *
  94  *
  95  * Arguments:   @const mpscan *m@ = pointer to bitscanner
  96  *
  97  * Returns:     The value of the current bit.
  98  *
  99  * Use:         Reads the value of the current bit looked at by a
 100  *              bitscanner.
 101  */
 102
 103 #define MPSCAN_BIT(m) ((m)->w & 1)
 104
 105 extern int mpscan_bit(const mpscan */*m*/);
 106
 107 /*----- Left-to right-scanning --------------------------------------------*/
 108
 109 /* --- @mpscan_rinitx@ --- *
 110  *
 111  * Arguments:   @mpscan *m@ = pointer to bitscanner structure
 112  *              @const mpw *v, *vl@ = vector of words to scan
 113  *
 114  * Returns:     ---
 115  *
 116  * Use:         Initializes a reverse bitscanner from a low-level
 117  *              vector-and-length representation of an integer.  Initially no
 118  *              bit is ready; you must call @mpscan_rstep@ before anything
 119  *              useful will come out.
 120  */
 121
 122 #define MPSCAN_RINITX(m_, v_, vl_) do {                                 \
 123   mpscan *_m = (m_);                                                    \
 124   _m->v = (v_);                                                         \
 125   _m->vl = (vl_);                                                       \
 126   while (_m->vl > _m->v && !_m->vl[-1])                                 \
 127     _m->vl--;                                                           \
 128   _m->bits = 0;                                                         \
 129 } while (0)
 130
 131 extern void mpscan_rinitx(mpscan */*m*/,
 132                           const mpw */*v*/, const mpw */*vl*/);
 133
 134 /* --- @mpscan_rstep@ --- *
 135  *
 136  * Arguments:   @mpscan *m@ = pointer to bitscanner
 137  *
 138  * Returns:     Nonzero if there is another bit to read.
 139  *
 140  * Use:         Steps on to the next bit in the integer.  The macro version
 141  *              evaluates its argument multiple times.
 142  */
 143
 144 #define MPSCAN_RSTEP(m)                                                 \
 145   ((m)->bits ? ((m)->w <<= 1, (m)->bits--, 1) :                         \
 146    (m)->vl > (m)->v ? ((m)->w = *--(m)->vl,                             \
 147                        (m)->bits = MPW_BITS - 1, 1) :                   \
 148    0)
 149
 150 extern int mpscan_rstep(mpscan */*m*/);
 151
 152 /* --- @mpscan_rbit@ --- *
 153  *
 154  * Arguments:   @const mpscan *m@ = pointer to bitscanner
 155  *
 156  * Returns:     The value of the current bit.
 157  *
 158  * Use:         Reads the value of the current bit looked at by a
 159  *              reverse bitscanner.
 160  */
 161
 162 #define MPSCAN_RBIT(m) (((m)->w >> (MPW_BITS - 1)) & 1)
 163
 164 extern int mpscan_rbit(const mpscan */*m*/);
 165
 166 /*----- That's all, folks -------------------------------------------------*/
 167
 168 #ifdef __cplusplus
 169   }
 170 #endif
 171
 172 #endif