libhed/expr.h

   1 /* The expression evaluator */
   2
   3 /* This is a libhed PUBLIC file.
   4  * This header file will be installed on the target system.
   5  * When you add new things here, make sure they start with hed_.
   6  */
   7
   8 /*
   9  * hed - Hexadecimal editor
  10  * Copyright (C) 2004  Petr Baudis <pasky@ucw.cz>
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of version 2 of the GNU General Public License as
  14  * published by the Free Software Foundation.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  * GNU General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU General Public License
  22  * along with this program; if not, write to the Free Software
  23  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  24  */
  25
  26 #ifndef LIBHED__EXPR_H
  27 #define LIBHED__EXPR_H
  28
  29 #include <libhed/types.h>
  30
  31 /*******************************************************************
  32  * BYTE STRINGS
  33  */
  34
  35 hed_off_t hed_bytestr2off(unsigned char *bytestr, size_t len, long flags);
  36 void hed_off2bytestr(unsigned char *bytestr, size_t len, hed_off_t num);
  37
  38 /*******************************************************************
  39  * EXPRESSIONS
  40  */
  41
  42 typedef long (*hed_expr_reg_cb)(void *data, char reg, hed_off_t ofs, /*  */
  43                                 unsigned char *scramble, size_t len);
  44 typedef long (*hed_expr_mark_cb)(void *data, char mark,
  45                                  unsigned char *scramble, size_t len);
  46
  47 struct hed_expr {
  48         struct hed_list_head atoms;
  49         size_t len;
  50         unsigned char *buf;
  51         hed_expr_reg_cb reg_cb;
  52         hed_expr_mark_cb mark_cb;
  53         void *cb_data;
  54         size_t cb_pos;
  55         long flags;
  56 };
  57
  58 /* Return flags for callbacks */
  59 #define HED_AEF_NEGATIVE 1      // the result should be treated as negative
  60 #define HED_AEF_SIGNED   2      // take the sign bit from the result
  61 #define HED_AEF_DYNAMIC  4      // result is not constant
  62
  63 #define HED_AEF_ENDIANMASK      (3<<3)  // endianity mask
  64 #define HED_AEF_KEEPENDIAN      (0<<3)  // keep endianity (no change)
  65 #define HED_AEF_FORCELE         (1<<3)  // force little-endian
  66 #define HED_AEF_FORCEBE         (2<<3)  // force big-endian
  67 #define HED_AEF_SWAPENDIAN      (3<<3)  // always swap endianity
  68
  69 #define HED_AEF_ERROR   (~(~0UL>>1))
  70
  71 /* NB: The HED_AEF_NEGATIVE flag behaves as an extra "hidden" MSB bit,
  72  * which is used in calculations, but not included in the final result.
  73  * This allows to fit unsigned values in the range 0..2^n-1 as well as
  74  * signed values from -2^(n-1)..2^(n-1)-1 into only n bits.
  75  *
  76  * In particular, a zero with HED_AEF_NEGATIVE set is not treated as
  77  * a negative zero, but rather as the largest negative signed value,
  78  * e.g. "00" byte string with HED_AEF_NEGATIVE represents -256.
  79  *
  80  * HED_AEF_NEGATIVE takes precedence over HED_AEF_SIGNED. The following
  81  * table shows the relation betwen the various bits and the resulting sign:
  82  *
  83  *   HED_AEF_NEGATIVE  HED_AEF_SIGNED  MSB  result
  84  *      0                 0             x   positive
  85  *      0                 1             0   positive
  86  *      0                 1             1   negative
  87  *      1                 x             x   negative
  88  */
  89
  90 struct hed_expr *hed_expr_new(char *sexpr,
  91                               hed_expr_reg_cb reg_cb,
  92                               hed_expr_mark_cb mark_cb,
  93                               void *cb_data);
  94 long hed_expr_eval(struct hed_expr *expr);
  95 void hed_expr_free(struct hed_expr *expr);
  96
  97 static inline size_t
  98 hed_expr_len(const struct hed_expr *expr)
  99 {
 100         return expr->len;
 101 }
 102
 103 static inline unsigned char *
 104 hed_expr_buf(const struct hed_expr *expr)
 105 {
 106         return expr->buf;
 107 }
 108
 109 static inline long
 110 hed_expr_flags(const struct hed_expr *expr)
 111 {
 112         return expr->flags;
 113 }
 114
 115 static inline hed_off_t
 116 hed_expr2off(const struct hed_expr *expr)
 117 {
 118         return hed_bytestr2off(hed_expr_buf(expr), hed_expr_len(expr),
 119                                hed_expr_flags(expr));
 120 }
 121
 122 #endif