LLVM  4.0.0
LEB128.h
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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 
19 
20 namespace llvm {
21 
22 /// Utility function to encode a SLEB128 value to an output stream.
23 inline void encodeSLEB128(int64_t Value, raw_ostream &OS) {
24  bool More;
25  do {
26  uint8_t Byte = Value & 0x7f;
27  // NOTE: this assumes that this signed shift is an arithmetic right shift.
28  Value >>= 7;
29  More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
30  ((Value == -1) && ((Byte & 0x40) != 0))));
31  if (More)
32  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
33  OS << char(Byte);
34  } while (More);
35 }
36 
37 /// Utility function to encode a ULEB128 value to an output stream.
38 inline void encodeULEB128(uint64_t Value, raw_ostream &OS,
39  unsigned Padding = 0) {
40  do {
41  uint8_t Byte = Value & 0x7f;
42  Value >>= 7;
43  if (Value != 0 || Padding != 0)
44  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
45  OS << char(Byte);
46  } while (Value != 0);
47 
48  // Pad with 0x80 and emit a null byte at the end.
49  if (Padding != 0) {
50  for (; Padding != 1; --Padding)
51  OS << '\x80';
52  OS << '\x00';
53  }
54 }
55 
56 /// Utility function to encode a ULEB128 value to a buffer. Returns
57 /// the length in bytes of the encoded value.
58 inline unsigned encodeULEB128(uint64_t Value, uint8_t *p,
59  unsigned Padding = 0) {
60  uint8_t *orig_p = p;
61  do {
62  uint8_t Byte = Value & 0x7f;
63  Value >>= 7;
64  if (Value != 0 || Padding != 0)
65  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
66  *p++ = Byte;
67  } while (Value != 0);
68 
69  // Pad with 0x80 and emit a null byte at the end.
70  if (Padding != 0) {
71  for (; Padding != 1; --Padding)
72  *p++ = '\x80';
73  *p++ = '\x00';
74  }
75  return (unsigned)(p - orig_p);
76 }
77 
78 
79 /// Utility function to decode a ULEB128 value.
80 inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr) {
81  const uint8_t *orig_p = p;
82  uint64_t Value = 0;
83  unsigned Shift = 0;
84  do {
85  Value += uint64_t(*p & 0x7f) << Shift;
86  Shift += 7;
87  } while (*p++ >= 128);
88  if (n)
89  *n = (unsigned)(p - orig_p);
90  return Value;
91 }
92 
93 /// Utility function to decode a SLEB128 value.
94 inline int64_t decodeSLEB128(const uint8_t *p, unsigned *n = nullptr) {
95  const uint8_t *orig_p = p;
96  int64_t Value = 0;
97  unsigned Shift = 0;
98  uint8_t Byte;
99  do {
100  Byte = *p++;
101  Value |= ((Byte & 0x7f) << Shift);
102  Shift += 7;
103  } while (Byte >= 128);
104  // Sign extend negative numbers.
105  if (Byte & 0x40)
106  Value |= (-1ULL) << Shift;
107  if (n)
108  *n = (unsigned)(p - orig_p);
109  return Value;
110 }
111 
112 
113 /// Utility function to get the size of the ULEB128-encoded value.
114 extern unsigned getULEB128Size(uint64_t Value);
115 
116 /// Utility function to get the size of the SLEB128-encoded value.
117 extern unsigned getSLEB128Size(int64_t Value);
118 
119 } // namespace llvm
120 
121 #endif // LLVM_SYSTEM_LEB128_H
uint64_t decodeULEB128(const uint8_t *p, unsigned *n=nullptr)
Utility function to decode a ULEB128 value.
Definition: LEB128.h:80
int64_t decodeSLEB128(const uint8_t *p, unsigned *n=nullptr)
Utility function to decode a SLEB128 value.
Definition: LEB128.h:94
unsigned getULEB128Size(uint64_t Value)
Utility function to get the size of the ULEB128-encoded value.
Definition: LEB128.cpp:20
void encodeSLEB128(int64_t Value, raw_ostream &OS)
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:30
LLVM Value Representation.
Definition: Value.h:71
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:44
void encodeULEB128(uint64_t Value, raw_ostream &OS, unsigned Padding=0)
Utility function to encode a ULEB128 value to an output stream.
Definition: LEB128.h:38