include/leb128.h

   1 /* Utilities for reading leb128 values.
   2    Copyright (C) 2012 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 #ifndef LEB128_H
  25 #define LEB128_H
  26
  27 /* Get a definition for inline.  */
  28 #include "ansidecl.h"
  29
  30 /* Get a definition for NULL, size_t.  */
  31 #include <stddef.h>
  32
  33 /* Decode the unsigned LEB128 constant at BUF into the variable pointed to
  34    by R, and return the number of bytes read.
  35    If we read off the end of the buffer, zero is returned,
  36    and nothing is stored in R.
  37
  38    Note: The result is an int instead of a pointer to the next byte to be
  39    read to avoid const-vs-non-const problems.  */
  40
  41 static inline size_t
  42 read_uleb128_to_ull (const unsigned char *buf, const unsigned char *buf_end,
  43                      unsigned long long *r)
  44 {
  45   const unsigned char *p = buf;
  46   unsigned int shift = 0;
  47   unsigned long long result = 0;
  48   unsigned char byte;
  49
  50   while (1)
  51     {
  52       if (p >= buf_end)
  53         return 0;
  54
  55       byte = *p++;
  56       result |= ((unsigned long long) (byte & 0x7f)) << shift;
  57       if ((byte & 0x80) == 0)
  58         break;
  59       shift += 7;
  60     }
  61
  62   *r = result;
  63   return p - buf;
  64 }
  65
  66 /* Decode the signed LEB128 constant at BUF into the variable pointed to
  67    by R, and return the number of bytes read.
  68    If we read off the end of the buffer, zero is returned,
  69    and nothing is stored in R.
  70
  71    Note: The result is an int instead of a pointer to the next byte to be
  72    read to avoid const-vs-non-const problems.  */
  73
  74 static inline size_t
  75 read_sleb128_to_ll (const unsigned char *buf, const unsigned char *buf_end,
  76                     long long *r)
  77 {
  78   const unsigned char *p = buf;
  79   unsigned int shift = 0;
  80   long long result = 0;
  81   unsigned char byte;
  82
  83   while (1)
  84     {
  85       if (p >= buf_end)
  86         return 0;
  87
  88       byte = *p++;
  89       result |= ((unsigned long long) (byte & 0x7f)) << shift;
  90       shift += 7;
  91       if ((byte & 0x80) == 0)
  92         break;
  93     }
  94   if (shift < (sizeof (*r) * 8) && (byte & 0x40) != 0)
  95     result |= -(((unsigned long long) 1) << shift);
  96
  97   *r = result;
  98   return p - buf;
  99 }
 100
 101 /* Return the number of bytes to read to skip past an LEB128 number in BUF.
 102    If the end isn't found before reaching BUF_END, return zero.
 103
 104    Note: The result is an int instead of a pointer to the next byte to be
 105    read to avoid const-vs-non-const problems.  */
 106
 107 static inline size_t
 108 skip_leb128 (const unsigned char *buf, const unsigned char *buf_end)
 109 {
 110   const unsigned char *p = buf;
 111   unsigned char byte;
 112
 113   while (1)
 114     {
 115       if (p == buf_end)
 116         return 0;
 117
 118       byte = *p++;
 119       if ((byte & 0x80) == 0)
 120         return p - buf;
 121     }
 122 }
 123
 124 #endif /* LEB128_H */