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
20namespace llvm {
21
22/// Utility function to encode a SLEB128 value to an output stream.
23inline 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.
38inline 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.
58inline 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.
80inline 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.
94extern unsigned getULEB128Size(uint64_t Value);
95
96/// Utility function to get the size of the SLEB128-encoded value.
97extern unsigned getSLEB128Size(int64_t Value);
98
99}  // namespace llvm
100
101#endif  // LLVM_SYSTEM_LEB128_H
102