Bitcoin Core  22.99.0
P2P Digital Currency
asmap.cpp
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1 // Copyright (c) 2019-2020 The Bitcoin Core developers
2 // Distributed under the MIT software license, see the accompanying
3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
4 
5 #include <map>
6 #include <vector>
7 #include <assert.h>
8 #include <crypto/common.h>
9 
10 namespace {
11 
12 constexpr uint32_t INVALID = 0xFFFFFFFF;
13 
14 uint32_t DecodeBits(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos, uint8_t minval, const std::vector<uint8_t> &bit_sizes)
15 {
16  uint32_t val = minval;
17  bool bit;
18  for (std::vector<uint8_t>::const_iterator bit_sizes_it = bit_sizes.begin();
19  bit_sizes_it != bit_sizes.end(); ++bit_sizes_it) {
20  if (bit_sizes_it + 1 != bit_sizes.end()) {
21  if (bitpos == endpos) break;
22  bit = *bitpos;
23  bitpos++;
24  } else {
25  bit = 0;
26  }
27  if (bit) {
28  val += (1 << *bit_sizes_it);
29  } else {
30  for (int b = 0; b < *bit_sizes_it; b++) {
31  if (bitpos == endpos) return INVALID; // Reached EOF in mantissa
32  bit = *bitpos;
33  bitpos++;
34  val += bit << (*bit_sizes_it - 1 - b);
35  }
36  return val;
37  }
38  }
39  return INVALID; // Reached EOF in exponent
40 }
41 
42 enum class Instruction : uint32_t
43 {
44  RETURN = 0,
45  JUMP = 1,
46  MATCH = 2,
47  DEFAULT = 3,
48 };
49 
50 const std::vector<uint8_t> TYPE_BIT_SIZES{0, 0, 1};
51 Instruction DecodeType(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
52 {
53  return Instruction(DecodeBits(bitpos, endpos, 0, TYPE_BIT_SIZES));
54 }
55 
56 const std::vector<uint8_t> ASN_BIT_SIZES{15, 16, 17, 18, 19, 20, 21, 22, 23, 24};
57 uint32_t DecodeASN(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
58 {
59  return DecodeBits(bitpos, endpos, 1, ASN_BIT_SIZES);
60 }
61 
62 
63 const std::vector<uint8_t> MATCH_BIT_SIZES{1, 2, 3, 4, 5, 6, 7, 8};
64 uint32_t DecodeMatch(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
65 {
66  return DecodeBits(bitpos, endpos, 2, MATCH_BIT_SIZES);
67 }
68 
69 
70 const std::vector<uint8_t> JUMP_BIT_SIZES{5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30};
71 uint32_t DecodeJump(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
72 {
73  return DecodeBits(bitpos, endpos, 17, JUMP_BIT_SIZES);
74 }
75 
76 }
77 
78 uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip)
79 {
80  std::vector<bool>::const_iterator pos = asmap.begin();
81  const std::vector<bool>::const_iterator endpos = asmap.end();
82  uint8_t bits = ip.size();
83  uint32_t default_asn = 0;
84  uint32_t jump, match, matchlen;
85  Instruction opcode;
86  while (pos != endpos) {
87  opcode = DecodeType(pos, endpos);
88  if (opcode == Instruction::RETURN) {
89  default_asn = DecodeASN(pos, endpos);
90  if (default_asn == INVALID) break; // ASN straddles EOF
91  return default_asn;
92  } else if (opcode == Instruction::JUMP) {
93  jump = DecodeJump(pos, endpos);
94  if (jump == INVALID) break; // Jump offset straddles EOF
95  if (bits == 0) break; // No input bits left
96  if (int64_t{jump} >= int64_t{endpos - pos}) break; // Jumping past EOF
97  if (ip[ip.size() - bits]) {
98  pos += jump;
99  }
100  bits--;
101  } else if (opcode == Instruction::MATCH) {
102  match = DecodeMatch(pos, endpos);
103  if (match == INVALID) break; // Match bits straddle EOF
104  matchlen = CountBits(match) - 1;
105  if (bits < matchlen) break; // Not enough input bits
106  for (uint32_t bit = 0; bit < matchlen; bit++) {
107  if ((ip[ip.size() - bits]) != ((match >> (matchlen - 1 - bit)) & 1)) {
108  return default_asn;
109  }
110  bits--;
111  }
112  } else if (opcode == Instruction::DEFAULT) {
113  default_asn = DecodeASN(pos, endpos);
114  if (default_asn == INVALID) break; // ASN straddles EOF
115  } else {
116  break; // Instruction straddles EOF
117  }
118  }
119  assert(false); // Reached EOF without RETURN, or aborted (see any of the breaks above) - should have been caught by SanityCheckASMap below
120  return 0; // 0 is not a valid ASN
121 }
122 
123 bool SanityCheckASMap(const std::vector<bool>& asmap, int bits)
124 {
125  const std::vector<bool>::const_iterator begin = asmap.begin(), endpos = asmap.end();
126  std::vector<bool>::const_iterator pos = begin;
127  std::vector<std::pair<uint32_t, int>> jumps; // All future positions we may jump to (bit offset in asmap -> bits to consume left)
128  jumps.reserve(bits);
129  Instruction prevopcode = Instruction::JUMP;
130  bool had_incomplete_match = false;
131  while (pos != endpos) {
132  uint32_t offset = pos - begin;
133  if (!jumps.empty() && offset >= jumps.back().first) return false; // There was a jump into the middle of the previous instruction
134  Instruction opcode = DecodeType(pos, endpos);
135  if (opcode == Instruction::RETURN) {
136  if (prevopcode == Instruction::DEFAULT) return false; // There should not be any RETURN immediately after a DEFAULT (could be combined into just RETURN)
137  uint32_t asn = DecodeASN(pos, endpos);
138  if (asn == INVALID) return false; // ASN straddles EOF
139  if (jumps.empty()) {
140  // Nothing to execute anymore
141  if (endpos - pos > 7) return false; // Excessive padding
142  while (pos != endpos) {
143  if (*pos) return false; // Nonzero padding bit
144  ++pos;
145  }
146  return true; // Sanely reached EOF
147  } else {
148  // Continue by pretending we jumped to the next instruction
149  offset = pos - begin;
150  if (offset != jumps.back().first) return false; // Unreachable code
151  bits = jumps.back().second; // Restore the number of bits we would have had left after this jump
152  jumps.pop_back();
153  prevopcode = Instruction::JUMP;
154  }
155  } else if (opcode == Instruction::JUMP) {
156  uint32_t jump = DecodeJump(pos, endpos);
157  if (jump == INVALID) return false; // Jump offset straddles EOF
158  if (int64_t{jump} > int64_t{endpos - pos}) return false; // Jump out of range
159  if (bits == 0) return false; // Consuming bits past the end of the input
160  --bits;
161  uint32_t jump_offset = pos - begin + jump;
162  if (!jumps.empty() && jump_offset >= jumps.back().first) return false; // Intersecting jumps
163  jumps.emplace_back(jump_offset, bits);
164  prevopcode = Instruction::JUMP;
165  } else if (opcode == Instruction::MATCH) {
166  uint32_t match = DecodeMatch(pos, endpos);
167  if (match == INVALID) return false; // Match bits straddle EOF
168  int matchlen = CountBits(match) - 1;
169  if (prevopcode != Instruction::MATCH) had_incomplete_match = false;
170  if (matchlen < 8 && had_incomplete_match) return false; // Within a sequence of matches only at most one should be incomplete
171  had_incomplete_match = (matchlen < 8);
172  if (bits < matchlen) return false; // Consuming bits past the end of the input
173  bits -= matchlen;
174  prevopcode = Instruction::MATCH;
175  } else if (opcode == Instruction::DEFAULT) {
176  if (prevopcode == Instruction::DEFAULT) return false; // There should not be two successive DEFAULTs (they could be combined into one)
177  uint32_t asn = DecodeASN(pos, endpos);
178  if (asn == INVALID) return false; // ASN straddles EOF
179  prevopcode = Instruction::DEFAULT;
180  } else {
181  return false; // Instruction straddles EOF
182  }
183  }
184  return false; // Reached EOF without RETURN instruction
185 }
SanityCheckASMap
bool SanityCheckASMap(const std::vector< bool > &asmap, int bits)
Definition: asmap.cpp:123
assert
assert(!tx.IsCoinBase())
common.h
bech32::Encoding::INVALID
@ INVALID
Failed decoding.
Interpret
uint32_t Interpret(const std::vector< bool > &asmap, const std::vector< bool > &ip)
Definition: asmap.cpp:78
VarIntMode::DEFAULT
@ DEFAULT
CountBits
static uint64_t CountBits(uint64_t x)
Return the smallest number n such that (x >> n) == 0 (or 64 if the highest bit in x is set.
Definition: common.h:90