LLVM 17.0.0git
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
19namespace llvm {
20
21/// Utility function to encode a SLEB128 value to an output stream. Returns
22/// the length in bytes of the encoded value.
23inline 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.
52inline 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.
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.
104inline 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.
128inline 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 (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 != 0) || 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 += Slice << 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.
161inline 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 (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 uint64_t Slice = Byte & 0x7f;
180 if ((Shift >= 64 && Slice != (Value < 0 ? 0x7f : 0x00)) ||
181 (Shift == 63 && Slice != 0 && Slice != 0x7f)) {
182 if (error)
183 *error = "sleb128 too big for int64";
184 if (n)
185 *n = (unsigned)(p - orig_p);
186 return 0;
187 }
188 Value |= Slice << Shift;
189 Shift += 7;
190 ++p;
191 } while (Byte >= 128);
192 // Sign extend negative numbers if needed.
193 if (Shift < 64 && (Byte & 0x40))
194 Value |= UINT64_MAX << Shift;
195 if (n)
196 *n = (unsigned)(p - orig_p);
197 return Value;
198}
199
200/// Utility function to get the size of the ULEB128-encoded value.
201extern unsigned getULEB128Size(uint64_t Value);
202
203/// Utility function to get the size of the SLEB128-encoded value.
204extern unsigned getSLEB128Size(int64_t Value);
205
206} // namespace llvm
207
208#endif // LLVM_SUPPORT_LEB128_H
raw_pwrite_stream & OS
#define error(X)
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:52
#define UINT64_MAX
Definition: DataTypes.h:77
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
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
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
unsigned getULEB128Size(uint64_t Value)
Utility function to get the size of the ULEB128-encoded value.
Definition: LEB128.cpp:19
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 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 getSLEB128Size(int64_t Value)
Utility function to get the size of the SLEB128-encoded value.
Definition: LEB128.cpp:29