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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 
18 #include "llvm/Support/raw_ostream.h"
19 
20 namespace llvm {
21 
22 /// Utility function to encode a SLEB128 value to an output stream.
encodeSLEB128(int64_t Value,raw_ostream & OS)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 += (*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 get the size of the ULEB128-encoded value.
94 extern unsigned getULEB128Size(uint64_t Value);
95 
96 /// Utility function to get the size of the SLEB128-encoded value.
97 extern unsigned getSLEB128Size(int64_t Value);
98 
99 }  // namespace llvm
100 
101 #endif  // LLVM_SYSTEM_LEB128_H
102