mdw@git.distorted.org.uk Git - catacomb/blob - symm/ocb.h

   1 /* -*-c-*-
   2  *
   3  * Common definitions for OCB and related modes
   4  *
   5  * (c) 2018 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 it
  13  * under the terms of the GNU Library General Public License as published
  14  * by the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful, but
  18  * WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  20  * 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 Software
  24  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  25  * USA.
  26  */
  27
  28 #ifndef CATACOMB_OCB_H
  29 #define CATACOMB_OCB_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Header files ------------------------------------------------------*/
  36
  37 #include <stddef.h>
  38
  39 #include <mLib/bits.h>
  40 #include <mLib/compiler.h>
  41
  42 /*----- Constants ---------------------------------------------------------*/
  43
  44 /* The number of offsets to maintain.  Rather than calculate and store all
  45  * possible offset values in advance, or calculate new ones on demand (and
  46  * have to allocate space for them), we calculate a number in advance, and
  47  * determine any others every time they're needed.  If we calculate the first
  48  * %$n$% offsets only, then we spend %$i - n + 1$% time calculating offset
  49  * %$L_i$% when %$i \ge n$%.  But the offset %$L_i$% is used only for a
  50  * %$2^{-i-1}$% fraction of the blocks.  Summing up this geometric series
  51  * shows us that we add only a small constant overhead, and save storage
  52  * space for many offsets.
  53  */
  54 #define OCB_NCALC 16
  55 #define OCB_CALCMASK ((1ul << OCB_NCALC) - 1)
  56
  57 /*----- Functions provided ------------------------------------------------*/
  58
  59 /* --- @ocb_ctz@, @ocb_ctzl@ --- *
  60  *
  61  * Arguments:   @unsigned i@ or @unsigned long i@ = operand, assumed nonzero
  62  *
  63  * Returns:     The number of trailing zero bits in @i@, or nonsense if
  64  *              %$i = 0$%.
  65  */
  66
  67 extern unsigned ocb_ctz(unsigned /*i*/);
  68 extern unsigned ocb_ctzl(unsigned long /*i*/);
  69
  70 #if GCC_VERSION_P(3, 4)
  71 #  define OCB_CTZ(i) __builtin_ctz(i)
  72 #  define OCB_CTZL(i) __builtin_ctzl(i)
  73 #else
  74 #  define OCB_CTZ(i) ocb_ctz(i)
  75 #  define OCB_CTZL(i) ocb_ctzl(i)
  76 #endif
  77
  78 /* --- @OCB_OFFSET@ --- *
  79  *
  80  * Arguments:   @PRE@ = block cipher prefix
  81  *              @uint32 *o@ = pointer to offset accumulator
  82  *              @uint32 (*l)[PRE_BLKSZ]@ = pointer to offset mask table
  83  *              @unsigned long i@ = block index
  84  *
  85  * Returns:     ---
  86  *
  87  * Use:         Update the per-block offset for Grey-code-based OCB
  88  *              variants.  On entry, @o@ is assumed to hold the offset for
  89  *              block @i - 1@; on exit @o@ is updated to hold the offset for
  90  *              block @i@.
  91  */
  92
  93 #define OCB_OFFSET(PRE, o, l, i) do {                                   \
  94   uint32 (*_l)[PRE##_BLKSZ/4] = (l);                                    \
  95   uint32 *_o = (o);                                                     \
  96   unsigned long _i = (i);                                               \
  97   unsigned _j;                                                          \
  98                                                                         \
  99   if (_i&OCB_CALCMASK) {                                                \
 100     _j = OCB_CTZ(_i);                                                   \
 101     BLKC_XMOVE(PRE, _o, _l[_j]);                                        \
 102   } else {                                                              \
 103     uint32 _t[PRE##_BLKSZ];                                             \
 104     _j = OCB_CTZL(_i) - OCB_NCALC;                                      \
 105     BLKC_BLSHIFT(PRE, IRRED, _t, _l[OCB_NCALC - 1]);                    \
 106     while (_j--) BLKC_BLSHIFT(PRE, IRRED, _t, _t);                      \
 107     BLKC_XMOVE(PRE, _t, _l[_j]);                                        \
 108   }                                                                     \
 109 } while (0)
 110
 111 /*----- That's all, folks -------------------------------------------------*/
 112
 113 #ifdef __cplusplus
 114   }
 115 #endif
 116
 117 #endif