include/leb128.h

   1 /* Utilities for reading leb128 values.
   2    Copyright (C) 2012-2021 Free Software Foundation, Inc.
   3
   4 This file is part of the libiberty library.
   5 Libiberty is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public
   7 License as published by the Free Software Foundation; either
   8 version 2 of the License, or (at your option) any later version.
   9
  10 Libiberty is distributed in the hope that it will be useful,
  11 but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with libiberty; see the file COPYING.LIB.  If not, write
  17 to the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
  18 Boston, MA 02110-1301, USA.  */
  19
  20 /* The functions defined here can be speed critical.
  21    Since they are all pretty small we keep things simple and just define
  22    them all as "static inline".
  23
  24    WARNING: This file is used by GDB which is stuck at C90. :-(
  25    Though it can use stdint.h, inttypes.h.
  26    Therefore if you want to add support for "long long" you need
  27    to wrap it in #ifdef CC_HAS_LONG_LONG.  */
  28
  29 #ifndef LEB128_H
  30 #define LEB128_H
  31
  32 /* Get a definition for inline.  */
  33 #include "ansidecl.h"
  34
  35 /* Get a definition for NULL, size_t.  */
  36 #include <stddef.h>
  37
  38 #ifdef HAVE_STDINT_H
  39 #include <stdint.h>
  40 #endif
  41 #ifdef HAVE_INTTYPES_H
  42 #include <inttypes.h>
  43 #endif
  44
  45 /* Decode the unsigned LEB128 constant at BUF into the variable pointed to
  46    by R, and return the number of bytes read.
  47    If we read off the end of the buffer, zero is returned,
  48    and nothing is stored in R.
  49
  50    Note: The result is an int instead of a pointer to the next byte to be
  51    read to avoid const-vs-non-const problems.  */
  52
  53 static inline size_t
  54 read_uleb128_to_uint64 (const unsigned char *buf, const unsigned char *buf_end,
  55                         uint64_t *r)
  56 {
  57   const unsigned char *p = buf;
  58   unsigned int shift = 0;
  59   uint64_t result = 0;
  60   unsigned char byte;
  61
  62   while (1)
  63     {
  64       if (p >= buf_end)
  65         return 0;
  66
  67       byte = *p++;
  68       result |= ((uint64_t) (byte & 0x7f)) << shift;
  69       if ((byte & 0x80) == 0)
  70         break;
  71       shift += 7;
  72     }
  73
  74   *r = result;
  75   return p - buf;
  76 }
  77
  78 /* Decode the signed LEB128 constant at BUF into the variable pointed to
  79    by R, and return the number of bytes read.
  80    If we read off the end of the buffer, zero is returned,
  81    and nothing is stored in R.
  82
  83    Note: The result is an int instead of a pointer to the next byte to be
  84    read to avoid const-vs-non-const problems.  */
  85
  86 static inline size_t
  87 read_sleb128_to_int64 (const unsigned char *buf, const unsigned char *buf_end,
  88                        int64_t *r)
  89 {
  90   const unsigned char *p = buf;
  91   unsigned int shift = 0;
  92   int64_t result = 0;
  93   unsigned char byte;
  94
  95   while (1)
  96     {
  97       if (p >= buf_end)
  98         return 0;
  99
 100       byte = *p++;
 101       result |= ((uint64_t) (byte & 0x7f)) << shift;
 102       shift += 7;
 103       if ((byte & 0x80) == 0)
 104         break;
 105     }
 106   if (shift < (sizeof (*r) * 8) && (byte & 0x40) != 0)
 107     result |= -(((uint64_t) 1) << shift);
 108
 109   *r = result;
 110   return p - buf;
 111 }
 112
 113 /* Return the number of bytes to read to skip past an LEB128 number in BUF.
 114    If the end isn't found before reaching BUF_END, return zero.
 115
 116    Note: The result is an int instead of a pointer to the next byte to be
 117    read to avoid const-vs-non-const problems.  */
 118
 119 static inline size_t
 120 skip_leb128 (const unsigned char *buf, const unsigned char *buf_end)
 121 {
 122   const unsigned char *p = buf;
 123   unsigned char byte;
 124
 125   while (1)
 126     {
 127       if (p == buf_end)
 128         return 0;
 129
 130       byte = *p++;
 131       if ((byte & 0x80) == 0)
 132         return p - buf;
 133     }
 134 }
 135
 136 #endif /* LEB128_H */