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
17 #include "llvm/Support/raw_ostream.h"
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 ///
129 /// If \p error is non-null, it will point to a static error message,
130 /// if an error occured. It will not be modified on success.
131 inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr,
132 const uint8_t *end = nullptr,
133 const char **error = nullptr) {
134 const uint8_t *orig_p = p;
135 uint64_t Value = 0;
136 unsigned Shift = 0;
137 do {
138 if (LLVM_UNLIKELY(p == end)) {
139 if (error)
140 *error = "malformed uleb128, extends past end";
141 Value = 0;
142 break;
143 }
144 uint64_t Slice = *p & 0x7f;
145 if (LLVM_UNLIKELY(Shift >= 63) &&
146 ((Shift == 63 && (Slice << Shift >> Shift) != Slice) ||
147 (Shift > 63 && Slice != 0))) {
148 if (error)
149 *error = "uleb128 too big for uint64";
150 Value = 0;
151 break;
152 }
153 Value += Slice << Shift;
154 Shift += 7;
155 } while (*p++ >= 128);
156 if (n)
157 *n = (unsigned)(p - orig_p);
158 return Value;
159 }
160
161 /// Utility function to decode a SLEB128 value.
162 ///
163 /// If \p error is non-null, it will point to a static error message,
164 /// if an error occured. It will not be modified on success.
165 inline int64_t decodeSLEB128(const uint8_t *p, unsigned *n = nullptr,
166 const uint8_t *end = nullptr,
167 const char **error = nullptr) {
168 const uint8_t *orig_p = p;
169 int64_t Value = 0;
170 unsigned Shift = 0;
171 uint8_t Byte;
172 do {
173 if (LLVM_UNLIKELY(p == end)) {
174 if (error)
175 *error = "malformed sleb128, extends past end";
176 if (n)
177 *n = (unsigned)(p - orig_p);
178 return 0;
179 }
180 Byte = *p;
181 uint64_t Slice = Byte & 0x7f;
182 if (LLVM_UNLIKELY(Shift >= 63) &&
183 ((Shift == 63 && Slice != 0 && Slice != 0x7f) ||
184 (Shift > 63 && Slice != (Value < 0 ? 0x7f : 0x00)))) {
185 if (error)
186 *error = "sleb128 too big for int64";
187 if (n)
188 *n = (unsigned)(p - orig_p);
189 return 0;
190 }
191 Value |= Slice << Shift;
192 Shift += 7;
193 ++p;
194 } while (Byte >= 128);
195 // Sign extend negative numbers if needed.
196 if (Shift < 64 && (Byte & 0x40))
197 Value |= UINT64_MAX << Shift;
198 if (n)
199 *n = (unsigned)(p - orig_p);
200 return Value;
201 }
202
203 inline uint64_t decodeULEB128AndInc(const uint8_t *&p, const uint8_t *end,
204 const char **error = nullptr) {
205 unsigned n;
206 auto ret = decodeULEB128(p, &n, end, error);
207 p += n;
208 return ret;
209 }
210
211 inline int64_t decodeSLEB128AndInc(const uint8_t *&p, const uint8_t *end,
212 const char **error = nullptr) {
213 unsigned n;
214 auto ret = decodeSLEB128(p, &n, end, error);
215 p += n;
216 return ret;
217 }
218
decodeULEB128AndIncUnsafe(const uint8_t * & p)219 inline uint64_t decodeULEB128AndIncUnsafe(const uint8_t *&p) {
220 return decodeULEB128AndInc(p, nullptr);
221 }
222
223 /// Utility function to get the size of the ULEB128-encoded value.
224 extern unsigned getULEB128Size(uint64_t Value);
225
226 /// Utility function to get the size of the SLEB128-encoded value.
227 extern unsigned getSLEB128Size(int64_t Value);
228
229 } // namespace llvm
230
231 #endif // LLVM_SUPPORT_LEB128_H
232