libsanitizer/sanitizer_common/sanitizer_leb128.h

   1 //===-- sanitizer_leb128.h --------------------------------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef SANITIZER_LEB128_H
  10 #define SANITIZER_LEB128_H
  11
  12 #include "sanitizer_common.h"
  13 #include "sanitizer_internal_defs.h"
  14
  15 namespace __sanitizer {
  16
  17 template <typename T, typename It>
  18 It EncodeSLEB128(T value, It begin, It end) {
  19   bool more;
  20   do {
  21     u8 byte = value & 0x7f;
  22     // NOTE: this assumes that this signed shift is an arithmetic right shift.
  23     value >>= 7;
  24     more = !((((value == 0) && ((byte & 0x40) == 0)) ||
  25               ((value == -1) && ((byte & 0x40) != 0))));
  26     if (more)
  27       byte |= 0x80;
  28     if (UNLIKELY(begin == end))
  29       break;
  30     *(begin++) = byte;
  31   } while (more);
  32   return begin;
  33 }
  34
  35 template <typename T, typename It>
  36 It DecodeSLEB128(It begin, It end, T* v) {
  37   T value = 0;
  38   unsigned shift = 0;
  39   u8 byte;
  40   do {
  41     if (UNLIKELY(begin == end))
  42       return begin;
  43     byte = *(begin++);
  44     T slice = byte & 0x7f;
  45     value |= slice << shift;
  46     shift += 7;
  47   } while (byte >= 128);
  48   if (shift < 64 && (byte & 0x40))
  49     value |= (-1ULL) << shift;
  50   *v = value;
  51   return begin;
  52 }
  53
  54 template <typename T, typename It>
  55 It EncodeULEB128(T value, It begin, It end) {
  56   do {
  57     u8 byte = value & 0x7f;
  58     value >>= 7;
  59     if (value)
  60       byte |= 0x80;
  61     if (UNLIKELY(begin == end))
  62       break;
  63     *(begin++) = byte;
  64   } while (value);
  65   return begin;
  66 }
  67
  68 template <typename T, typename It>
  69 It DecodeULEB128(It begin, It end, T* v) {
  70   T value = 0;
  71   unsigned shift = 0;
  72   u8 byte;
  73   do {
  74     if (UNLIKELY(begin == end))
  75       return begin;
  76     byte = *(begin++);
  77     T slice = byte & 0x7f;
  78     value += slice << shift;
  79     shift += 7;
  80   } while (byte >= 128);
  81   *v = value;
  82   return begin;
  83 }
  84
  85 }  // namespace __sanitizer
  86
  87 #endif  // SANITIZER_LEB128_H