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 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 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. 48 inline unsigned encodeSLEB128(int64_t Value, uint8_t *p, unsigned Padding = 0) { 49 uint8_t *orig_p = p; 50 bool More; 51 do { 52 uint8_t Byte = Value & 0x7f; 53 // NOTE: this assumes that this signed shift is an arithmetic right shift. 54 Value >>= 7; 55 More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) || 56 ((Value == -1) && ((Byte & 0x40) != 0)))); 57 if (More || Padding != 0) 58 Byte |= 0x80; // Mark this byte to show that more bytes will follow. 59 *p++ = Byte; 60 } while (More); 61 62 // Pad with 0x80 and emit a terminating byte at the end. 63 if (Padding != 0) { 64 uint8_t PadValue = Value < 0 ? 0x7f : 0x00; 65 for (; Padding != 1; --Padding) 66 *p++ = (PadValue | 0x80); 67 *p++ = PadValue; 68 } 69 return (unsigned)(p - orig_p); 70 } 71 72 /// Utility function to encode a ULEB128 value to an output stream. 73 inline void encodeULEB128(uint64_t Value, raw_ostream &OS, 74 unsigned Padding = 0) { 75 do { 76 uint8_t Byte = Value & 0x7f; 77 Value >>= 7; 78 if (Value != 0 || Padding != 0) 79 Byte |= 0x80; // Mark this byte to show that more bytes will follow. 80 OS << char(Byte); 81 } while (Value != 0); 82 83 // Pad with 0x80 and emit a null byte at the end. 84 if (Padding != 0) { 85 for (; Padding != 1; --Padding) 86 OS << '\x80'; 87 OS << '\x00'; 88 } 89 } 90 91 /// Utility function to encode a ULEB128 value to a buffer. Returns 92 /// the length in bytes of the encoded value. 93 inline unsigned encodeULEB128(uint64_t Value, uint8_t *p, 94 unsigned Padding = 0) { 95 uint8_t *orig_p = p; 96 do { 97 uint8_t Byte = Value & 0x7f; 98 Value >>= 7; 99 if (Value != 0 || Padding != 0) 100 Byte |= 0x80; // Mark this byte to show that more bytes will follow. 101 *p++ = Byte; 102 } while (Value != 0); 103 104 // Pad with 0x80 and emit a null byte at the end. 105 if (Padding != 0) { 106 for (; Padding != 1; --Padding) 107 *p++ = '\x80'; 108 *p++ = '\x00'; 109 } 110 return (unsigned)(p - orig_p); 111 } 112 113 /// Utility function to decode a ULEB128 value. 114 inline uint64_t decodeULEB128(const uint8_t *p, unsigned *n = nullptr, 115 const uint8_t *end = nullptr, 116 const char **error = nullptr) { 117 const uint8_t *orig_p = p; 118 uint64_t Value = 0; 119 unsigned Shift = 0; 120 if (error) 121 *error = nullptr; 122 do { 123 if (end && p == end) { 124 if (error) 125 *error = "malformed uleb128, extends past end"; 126 if (n) 127 *n = (unsigned)(p - orig_p); 128 return 0; 129 } 130 uint64_t Slice = *p & 0x7f; 131 if (Shift >= 64 || Slice << Shift >> Shift != Slice) { 132 if (error) 133 *error = "uleb128 too big for uint64"; 134 if (n) 135 *n = (unsigned)(p - orig_p); 136 return 0; 137 } 138 Value += uint64_t(*p & 0x7f) << Shift; 139 Shift += 7; 140 } while (*p++ >= 128); 141 if (n) 142 *n = (unsigned)(p - orig_p); 143 return Value; 144 } 145 146 /// Utility function to decode a SLEB128 value. 147 inline int64_t decodeSLEB128(const uint8_t *p, unsigned *n = nullptr, 148 const uint8_t *end = nullptr, 149 const char **error = nullptr) { 150 const uint8_t *orig_p = p; 151 int64_t Value = 0; 152 unsigned Shift = 0; 153 uint8_t Byte; 154 do { 155 if (end && p == end) { 156 if (error) 157 *error = "malformed sleb128, extends past end"; 158 if (n) 159 *n = (unsigned)(p - orig_p); 160 return 0; 161 } 162 Byte = *p++; 163 Value |= (int64_t(Byte & 0x7f) << Shift); 164 Shift += 7; 165 } while (Byte >= 128); 166 // Sign extend negative numbers. 167 if (Byte & 0x40) 168 Value |= (-1ULL) << Shift; 169 if (n) 170 *n = (unsigned)(p - orig_p); 171 return Value; 172 } 173 174 /// Utility function to get the size of the ULEB128-encoded value. 175 extern unsigned getULEB128Size(uint64_t Value); 176 177 /// Utility function to get the size of the SLEB128-encoded value. 178 extern unsigned getSLEB128Size(int64_t Value); 179 180 } // namespace llvm 181 182 #endif // LLVM_SYSTEM_LEB128_H 183
