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   1 /* -*-c-*-
   2  *
   3  * $Id: mpscan.h,v 1.4 2000/07/29 17:03:31 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 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: mpscan.h,v $
  33  * Revision 1.4  2000/07/29 17:03:31  mdw
  34  * Add support for left-to-right bitscanning, for use in modular
  35  * exponentiation.
  36  *
  37  * Revision 1.3  1999/12/10 23:29:48  mdw
  38  * Change header file guard names.
  39  *
  40  * Revision 1.2  1999/11/13 01:55:10  mdw
  41  * Fixed so that they compile.  Minor interface changes.
  42  *
  43  * Revision 1.1  1999/09/03 08:41:12  mdw
  44  * Initial import.
  45  *
  46  */
  47
  48 #ifndef CATACOMB_MPSCAN_H
  49 #define CATACOMB_MPSCAN_H
  50
  51 #ifdef __cplusplus
  52   extern "C" {
  53 #endif
  54
  55 /*----- Header files ------------------------------------------------------*/
  56
  57 #ifndef CATACOMB_MPW_H
  58 #  include "mpw.h"
  59 #endif
  60
  61 /*----- Data structures ---------------------------------------------------*/
  62
  63 typedef struct mpscan {
  64   const mpw *v, *vl;                    /* Vector of words to scan */
  65   mpw w;                                /* Current word to scan */
  66   int bits;                             /* Number of bits left in @w@ */
  67 } mpscan;
  68
  69 /*----- Right-to-left scanning --------------------------------------------*/
  70
  71 /* --- @mpscan_initx@ --- *
  72  *
  73  * Arguments:   @mpscan *m@ = pointer to bitscanner structure
  74  *              @const mpw *v, *vl@ = vector of words to scan
  75  *
  76  * Returns:     ---
  77  *
  78  * Use:         Initializes a bitscanner from a low-level base-and-limit
  79  *              representation of an integer.  Initially no bit is ready; you
  80  *              must call @mpscan_step@ before anything useful will come
  81  *              out.
  82  */
  83
  84 #define MPSCAN_INITX(m_, v_, vl_) do {                                  \
  85   mpscan *_m = (m_);                                                    \
  86   _m->v = (v_);                                                         \
  87   _m->vl = (vl_);                                                       \
  88   _m->bits = 0;                                                         \
  89 } while (0)
  90
  91 extern void mpscan_initx(mpscan */*m*/, const mpw */*v*/, const mpw */*vl*/);
  92
  93 /* --- @mpscan_step@ --- *
  94  *
  95  * Arguments:   @mpscan *m@ = pointer to bitscanner
  96  *
  97  * Returns:     Nonzero if there is another bit to read.
  98  *
  99  * Use:         Steps on to the next bit in the integer.  The macro version
 100  *              evaluates its argument multiple times.
 101  */
 102
 103 #define MPSCAN_STEP(m)                                                  \
 104   ((m)->bits ? ((m)->w >>= 1, (m)->bits--, 1) :                         \
 105    (m)->v < (m)->vl ? ((m)->w = *(m)->v++,                              \
 106                        (m)->bits = MPW_BITS - 1, 1) :                   \
 107    0)
 108
 109 extern int mpscan_step(mpscan */*m*/);
 110
 111 /* --- @mpscan_bit@ --- *
 112  *
 113  * Arguments:   @const mpscan *m@ = pointer to bitscanner
 114  *
 115  * Returns:     The value of the current bit.
 116  *
 117  * Use:         Reads the value of the current bit looked at by a
 118  *              bitscanner.
 119  */
 120
 121 #define MPSCAN_BIT(m) ((m)->w & 1)
 122
 123 extern int mpscan_bit(const mpscan */*m*/);
 124
 125 /*----- Left-to right-scanning --------------------------------------------*/
 126
 127 /* --- @mpscan_rinitx@ --- *
 128  *
 129  * Arguments:   @mpscan *m@ = pointer to bitscanner structure
 130  *              @const mpw *v, *vl@ = vector of words to scan
 131  *
 132  * Returns:     ---
 133  *
 134  * Use:         Initializes a reverse bitscanner from a low-level
 135  *              vector-and-length representation of an integer.  Initially no
 136  *              bit is ready; you must call @mpscan_rstep@ before anything
 137  *              useful will come out.
 138  */
 139
 140 #define MPSCAN_RINITX(m_, v_, vl_) do {                                 \
 141   mpscan *_m = (m_);                                                    \
 142   _m->v = (v_);                                                         \
 143   _m->vl = (vl_);                                                       \
 144   while (_m->vl > _m->v && !_m->vl[-1])                                 \
 145     _m->vl--;                                                           \
 146   _m->bits = 0;                                                         \
 147 } while (0)
 148
 149 extern void mpscan_rinitx(mpscan */*m*/,
 150                           const mpw */*v*/, const mpw */*vl*/);
 151
 152 /* --- @mpscan_rstep@ --- *
 153  *
 154  * Arguments:   @mpscan *m@ = pointer to bitscanner
 155  *
 156  * Returns:     Nonzero if there is another bit to read.
 157  *
 158  * Use:         Steps on to the next bit in the integer.  The macro version
 159  *              evaluates its argument multiple times.
 160  */
 161
 162 #define MPSCAN_RSTEP(m)                                                 \
 163   ((m)->bits ? ((m)->w <<= 1, (m)->bits--, 1) :                         \
 164    (m)->vl > (m)->v ? ((m)->w = *--(m)->vl,                             \
 165                        (m)->bits = MPW_BITS - 1, 1) :                   \
 166    0)
 167
 168 extern int mpscan_rstep(mpscan */*m*/);
 169
 170 /* --- @mpscan_rbit@ --- *
 171  *
 172  * Arguments:   @const mpscan *m@ = pointer to bitscanner
 173  *
 174  * Returns:     The value of the current bit.
 175  *
 176  * Use:         Reads the value of the current bit looked at by a
 177  *              reverse bitscanner.
 178  */
 179
 180 #define MPSCAN_RBIT(m) (((m)->w >> (MPW_BITS - 1)) & 1)
 181
 182 extern int mpscan_rbit(const mpscan */*m*/);
 183
 184 /*----- That's all, folks -------------------------------------------------*/
 185
 186 #ifdef __cplusplus
 187   }
 188 #endif
 189
 190 #endif