LLVM  10.0.0svn
LEB128.h
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1 //===- llvm/Support/LEB128.h - [SU]LEB128 utility functions -----*- 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 // This file declares some utility functions for encoding SLEB128 and
10 // ULEB128 values.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_SUPPORT_LEB128_H
15 #define LLVM_SUPPORT_LEB128_H
16 
18 
19 namespace llvm {
20 
21 /// Utility function to encode a SLEB128 value to an output stream. Returns
22 /// the length in bytes of the encoded value.
23 inline unsigned encodeSLEB128(int64_t Value, raw_ostream &OS,
24  unsigned PadTo = 0) {
25  bool More;
26  unsigned Count = 0;
27  do {
28  uint8_t Byte = Value & 0x7f;
29  // NOTE: this assumes that this signed shift is an arithmetic right shift.
30  Value >>= 7;
31  More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
32  ((Value == -1) && ((Byte & 0x40) != 0))));
33  Count++;
34  if (More || Count < PadTo)
35  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
36  OS << char(Byte);
37  } while (More);
38 
39  // Pad with 0x80 and emit a terminating byte at the end.
40  if (Count < PadTo) {
41  uint8_t PadValue = Value < 0 ? 0x7f : 0x00;
42  for (; Count < PadTo - 1; ++Count)
43  OS << char(PadValue | 0x80);
44  OS << char(PadValue);
45  Count++;
46  }
47  return Count;
48 }
49 
50 /// Utility function to encode a SLEB128 value to a buffer. Returns
51 /// the length in bytes of the encoded value.
52 inline unsigned encodeSLEB128(int64_t Value, uint8_t *p, unsigned PadTo = 0) {
53  uint8_t *orig_p = p;
54  unsigned Count = 0;
55  bool More;
56  do {
57  uint8_t Byte = Value & 0x7f;
58  // NOTE: this assumes that this signed shift is an arithmetic right shift.
59  Value >>= 7;
60  More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
61  ((Value == -1) && ((Byte & 0x40) != 0))));
62  Count++;
63  if (More || Count < PadTo)
64  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
65  *p++ = Byte;
66  } while (More);
67 
68  // Pad with 0x80 and emit a terminating byte at the end.
69  if (Count < PadTo) {
70  uint8_t PadValue = Value < 0 ? 0x7f : 0x00;
71  for (; Count < PadTo - 1; ++Count)
72  *p++ = (PadValue | 0x80);
73  *p++ = PadValue;
74  }
75  return (unsigned)(p - orig_p);
76 }
77 
78 /// Utility function to encode a ULEB128 value to an output stream. Returns
79 /// the length in bytes of the encoded value.
80 inline unsigned encodeULEB128(uint64_t Value, raw_ostream &OS,
81  unsigned PadTo = 0) {
82  unsigned Count = 0;
83  do {
84  uint8_t Byte = Value & 0x7f;
85  Value >>= 7;
86  Count++;
87  if (Value != 0 || Count < PadTo)
88  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
89  OS << char(Byte);
90  } while (Value != 0);
91 
92  // Pad with 0x80 and emit a null byte at the end.
93  if (Count < PadTo) {
94  for (; Count < PadTo - 1; ++Count)
95  OS << '\x80';
96  OS << '\x00';
97  Count++;
98  }
99  return Count;
100 }
101 
102 /// Utility function to encode a ULEB128 value to a buffer. Returns
103 /// the length in bytes of the encoded value.
104 inline unsigned encodeULEB128(uint64_t Value, uint8_t *p,
105  unsigned PadTo = 0) {
106  uint8_t *orig_p = p;
107  unsigned Count = 0;
108  do {
109  uint8_t Byte = Value & 0x7f;
110  Value >>= 7;
111  Count++;
112  if (Value != 0 || Count < PadTo)
113  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
114  *p++ = Byte;
115  } while (Value != 0);
116 
117  // Pad with 0x80 and emit a null byte at the end.
118  if (Count < PadTo) {
119  for (; Count < PadTo - 1; ++Count)
120  *p++ = '\x80';
121  *p++ = '\x00';
122  }
123 
124  return (unsigned)(p - orig_p);
125 }
126 
127 /// Utility function to decode a ULEB128 value.
128 inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr,
129  const uint8_t *end = nullptr,
130  const char **error = nullptr) {
131  const uint8_t *orig_p = p;
132  uint64_t Value = 0;
133  unsigned Shift = 0;
134  if (error)
135  *error = nullptr;
136  do {
137  if (end && p == end) {
138  if (error)
139  *error = "malformed uleb128, extends past end";
140  if (n)
141  *n = (unsigned)(p - orig_p);
142  return 0;
143  }
144  uint64_t Slice = *p & 0x7f;
145  if (Shift >= 64 || Slice << Shift >> Shift != Slice) {
146  if (error)
147  *error = "uleb128 too big for uint64";
148  if (n)
149  *n = (unsigned)(p - orig_p);
150  return 0;
151  }
152  Value += uint64_t(*p & 0x7f) << Shift;
153  Shift += 7;
154  } while (*p++ >= 128);
155  if (n)
156  *n = (unsigned)(p - orig_p);
157  return Value;
158 }
159 
160 /// Utility function to decode a SLEB128 value.
161 inline int64_t decodeSLEB128(const uint8_t *p, unsigned *n = nullptr,
162  const uint8_t *end = nullptr,
163  const char **error = nullptr) {
164  const uint8_t *orig_p = p;
165  int64_t Value = 0;
166  unsigned Shift = 0;
167  uint8_t Byte;
168  if (error)
169  *error = nullptr;
170  do {
171  if (end && p == end) {
172  if (error)
173  *error = "malformed sleb128, extends past end";
174  if (n)
175  *n = (unsigned)(p - orig_p);
176  return 0;
177  }
178  Byte = *p++;
179  Value |= (uint64_t(Byte & 0x7f) << Shift);
180  Shift += 7;
181  } while (Byte >= 128);
182  // Sign extend negative numbers if needed.
183  if (Shift < 64 && (Byte & 0x40))
184  Value |= (-1ULL) << Shift;
185  if (n)
186  *n = (unsigned)(p - orig_p);
187  return Value;
188 }
189 
190 /// Utility function to get the size of the ULEB128-encoded value.
191 extern unsigned getULEB128Size(uint64_t Value);
192 
193 /// Utility function to get the size of the SLEB128-encoded value.
194 extern unsigned getSLEB128Size(int64_t Value);
195 
196 } // namespace llvm
197 
198 #endif // LLVM_SYSTEM_LEB128_H
const_iterator end(StringRef path)
Get end iterator over path.
Definition: Path.cpp:233
This class represents lattice values for constants.
Definition: AllocatorList.h:23
#define error(X)
int64_t decodeSLEB128(const uint8_t *p, unsigned *n=nullptr, const uint8_t *end=nullptr, const char **error=nullptr)
Utility function to decode a SLEB128 value.
Definition: LEB128.h:161
uint64_t decodeULEB128(const uint8_t *p, unsigned *n=nullptr, const uint8_t *end=nullptr, const char **error=nullptr)
Utility function to decode a ULEB128 value.
Definition: LEB128.h:128
unsigned getULEB128Size(uint64_t Value)
Utility function to get the size of the ULEB128-encoded value.
Definition: LEB128.cpp:19
unsigned encodeULEB128(uint64_t Value, raw_ostream &OS, unsigned PadTo=0)
Utility function to encode a ULEB128 value to an output stream.
Definition: LEB128.h:80
unsigned encodeSLEB128(int64_t Value, raw_ostream &OS, unsigned PadTo=0)
Utility function to encode a SLEB128 value to an output stream.
Definition: LEB128.h:23
unsigned getSLEB128Size(int64_t Value)
Utility function to get the size of the SLEB128-encoded value.
Definition: LEB128.cpp:29
LLVM Value Representation.
Definition: Value.h:74
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:45