git.distorted.org.uk Git - u/mdw/catacomb/blob - math/mpscan.h

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