1//===- llvm/Support/LEB128.h - [SU]LEB128 utility functions -----*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file declares some utility functions for encoding SLEB128 and
11// ULEB128 values.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_SUPPORT_LEB128_H
16#define LLVM_SUPPORT_LEB128_H
17
18#include "llvm/Support/raw_ostream.h"
19
20namespace llvm {
21
22/// Utility function to encode a SLEB128 value to an output stream.
23inline void encodeSLEB128(int64_t Value, raw_ostream &OS,
24                          unsigned Padding = 0) {
25  bool More;
26  do {
27    uint8_t Byte = Value & 0x7f;
28    // NOTE: this assumes that this signed shift is an arithmetic right shift.
29    Value >>= 7;
30    More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
31              ((Value == -1) && ((Byte & 0x40) != 0))));
32    if (More || Padding != 0)
33      Byte |= 0x80; // Mark this byte to show that more bytes will follow.
34    OS << char(Byte);
35  } while (More);
36
37  // Pad with 0x80 and emit a terminating byte at the end.
38  if (Padding != 0) {
39    uint8_t PadValue = Value < 0 ? 0x7f : 0x00;
40    for (; Padding != 1; --Padding)
41      OS << char(PadValue | 0x80);
42    OS << char(PadValue);
43  }
44}
45
46/// Utility function to encode a SLEB128 value to a buffer. Returns
47/// the length in bytes of the encoded value.
48inline unsigned encodeSLEB128(int64_t Value, uint8_t *p,
49                              unsigned Padding = 0) {
50  uint8_t *orig_p = p;
51  bool More;
52  do {
53    uint8_t Byte = Value & 0x7f;
54    // NOTE: this assumes that this signed shift is an arithmetic right shift.
55    Value >>= 7;
56    More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
57              ((Value == -1) && ((Byte & 0x40) != 0))));
58    if (More || Padding != 0)
59      Byte |= 0x80; // Mark this byte to show that more bytes will follow.
60    *p++ = Byte;
61  } while (More);
62
63  // Pad with 0x80 and emit a terminating byte at the end.
64  if (Padding != 0) {
65    uint8_t PadValue = Value < 0 ? 0x7f : 0x00;
66    for (; Padding != 1; --Padding)
67      *p++ = (PadValue | 0x80);
68    *p++ = PadValue;
69  }
70  return (unsigned)(p - orig_p);
71}
72
73/// Utility function to encode a ULEB128 value to an output stream.
74inline void encodeULEB128(uint64_t Value, raw_ostream &OS,
75                          unsigned Padding = 0) {
76  do {
77    uint8_t Byte = Value & 0x7f;
78    Value >>= 7;
79    if (Value != 0 || Padding != 0)
80      Byte |= 0x80; // Mark this byte to show that more bytes will follow.
81    OS << char(Byte);
82  } while (Value != 0);
83
84  // Pad with 0x80 and emit a null byte at the end.
85  if (Padding != 0) {
86    for (; Padding != 1; --Padding)
87      OS << '\x80';
88    OS << '\x00';
89  }
90}
91
92/// Utility function to encode a ULEB128 value to a buffer. Returns
93/// the length in bytes of the encoded value.
94inline unsigned encodeULEB128(uint64_t Value, uint8_t *p,
95                              unsigned Padding = 0) {
96  uint8_t *orig_p = p;
97  do {
98    uint8_t Byte = Value & 0x7f;
99    Value >>= 7;
100    if (Value != 0 || Padding != 0)
101      Byte |= 0x80; // Mark this byte to show that more bytes will follow.
102    *p++ = Byte;
103  } while (Value != 0);
104
105  // Pad with 0x80 and emit a null byte at the end.
106  if (Padding != 0) {
107    for (; Padding != 1; --Padding)
108      *p++ = '\x80';
109    *p++ = '\x00';
110  }
111  return (unsigned)(p - orig_p);
112}
113
114
115/// Utility function to decode a ULEB128 value.
116inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr,
117                              const uint8_t *end = nullptr,
118                              const char **error = nullptr) {
119  const uint8_t *orig_p = p;
120  uint64_t Value = 0;
121  unsigned Shift = 0;
122  if(error)
123    *error = nullptr;
124  do {
125    if(end && p == end){
126      if(error)
127        *error = "malformed uleb128, extends past end";
128      if (n)
129        *n = (unsigned)(p - orig_p);
130      return 0;
131    }
132    uint64_t Slice = *p & 0x7f;
133    if(Shift >= 64 || Slice << Shift >> Shift != Slice){
134      if(error)
135        *error = "uleb128 too big for uint64";
136      if (n)
137        *n = (unsigned)(p - orig_p);
138      return 0;
139    }
140    Value += uint64_t(*p & 0x7f) << Shift;
141    Shift += 7;
142  } while (*p++ >= 128);
143  if (n)
144    *n = (unsigned)(p - orig_p);
145  return Value;
146}
147
148/// Utility function to decode a SLEB128 value.
149inline int64_t decodeSLEB128(const uint8_t *p, unsigned *n = nullptr,
150                             const uint8_t *end = nullptr,
151                             const char **error = nullptr) {
152  const uint8_t *orig_p = p;
153  int64_t Value = 0;
154  unsigned Shift = 0;
155  uint8_t Byte;
156  do {
157    if(end && p == end){
158      if(error)
159        *error = "malformed sleb128, extends past end";
160      if (n)
161        *n = (unsigned)(p - orig_p);
162      return 0;
163    }
164    Byte = *p++;
165    Value |= ((Byte & 0x7f) << Shift);
166    Shift += 7;
167  } while (Byte >= 128);
168  // Sign extend negative numbers.
169  if (Byte & 0x40)
170    Value |= (-1ULL) << Shift;
171  if (n)
172    *n = (unsigned)(p - orig_p);
173  return Value;
174}
175
176
177/// Utility function to get the size of the ULEB128-encoded value.
178extern unsigned getULEB128Size(uint64_t Value);
179
180/// Utility function to get the size of the SLEB128-encoded value.
181extern unsigned getSLEB128Size(int64_t Value);
182
183}  // namespace llvm
184
185#endif  // LLVM_SYSTEM_LEB128_H
186