gold/int_encoding.cc

   1 // int_encoding.cc -- variable length and unaligned integer encoding support.
   2
   3 // Copyright (C) 2009-2017 Free Software Foundation, Inc.
   4 // Written by Doug Kwan <dougkwan@google.com> by refactoring scattered
   5 // contents from other files in gold.  Original code written by Ian
   6 // Lance Taylor <iant@google.com> and Caleb Howe <cshowe@google.com>.
   7
   8 // This file is part of gold.
   9
  10 // This program is free software; you can redistribute it and/or modify
  11 // it under the terms of the GNU General Public License as published by
  12 // the Free Software Foundation; either version 3 of the License, or
  13 // (at your option) any later version.
  14
  15 // This program is distributed in the hope that it will be useful,
  16 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  17 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18 // GNU General Public License for more details.
  19
  20 // You should have received a copy of the GNU General Public License
  21 // along with this program; if not, write to the Free Software
  22 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  23 // MA 02110-1301, USA.
  24
  25 #include "gold.h"
  26
  27 #include <vector>
  28
  29 #include "int_encoding.h"
  30
  31 namespace gold {
  32
  33 // Read an unsigned LEB128 number.  Each byte contains 7 bits of
  34 // information, plus one bit saying whether the number continues or
  35 // not.  BYTE contains the first byte of the number, and is guaranteed
  36 // to have the continuation bit set.
  37
  38 uint64_t
  39 read_unsigned_LEB_128_x(const unsigned char* buffer, size_t* len,
  40                         unsigned char byte)
  41 {
  42   uint64_t result = static_cast<uint64_t>(byte & 0x7f);
  43   size_t num_read = 1;
  44   unsigned int shift = 7;
  45
  46   do
  47     {
  48       if (num_read > 64 / 7 + 1)
  49         {
  50           gold_warning(_("Unusually large LEB128 decoded, "
  51                          "debug information may be corrupted"));
  52           break;
  53         }
  54       byte = *buffer++;
  55       num_read++;
  56       result |= (static_cast<uint64_t>(byte & 0x7f)) << shift;
  57       shift += 7;
  58     }
  59   while (byte & 0x80);
  60
  61   *len = num_read;
  62
  63   return result;
  64 }
  65
  66 // Read a signed LEB128 number.  These are like regular LEB128
  67 // numbers, except the last byte may have a sign bit set.
  68 // BYTE contains the first byte of the number, and is guaranteed
  69 // to have the continuation bit set.
  70
  71 int64_t
  72 read_signed_LEB_128_x(const unsigned char* buffer, size_t* len,
  73                       unsigned char byte)
  74 {
  75   int64_t result = static_cast<uint64_t>(byte & 0x7f);
  76   int shift = 7;
  77   size_t num_read = 1;
  78
  79   do
  80     {
  81       if (num_read > 64 / 7 + 1)
  82         {
  83           gold_warning(_("Unusually large LEB128 decoded, "
  84                          "debug information may be corrupted"));
  85           break;
  86         }
  87       byte = *buffer++;
  88       num_read++;
  89       result |= (static_cast<uint64_t>(byte & 0x7f) << shift);
  90       shift += 7;
  91     }
  92   while (byte & 0x80);
  93
  94   if ((shift < 8 * static_cast<int>(sizeof(result))) && (byte & 0x40))
  95     result |= -((static_cast<int64_t>(1)) << shift);
  96   *len = num_read;
  97   return result;
  98 }
  99
 100 void
 101 write_unsigned_LEB_128(std::vector<unsigned char>* buffer, uint64_t value)
 102 {
 103   do
 104     {
 105       unsigned char current_byte = value & 0x7f;
 106       value >>= 7;
 107       if (value != 0)
 108         {
 109           current_byte |= 0x80;
 110         }
 111       buffer->push_back(current_byte);
 112     }
 113   while (value != 0);
 114 }
 115
 116 size_t
 117 get_length_as_unsigned_LEB_128(uint64_t value)
 118 {
 119   size_t length = 0;
 120   do
 121     {
 122       unsigned char current_byte = value & 0x7f;
 123       value >>= 7;
 124       if (value != 0)
 125         {
 126           current_byte |= 0x80;
 127         }
 128       length++;
 129     }
 130   while (value != 0);
 131   return length;
 132 }
 133
 134 } // End namespace gold.