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src/util/asmap.cpp
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// Copyright (c) 2019 The Bitcoin Core developers | |||||
// Distributed under the MIT software license, see the accompanying | |||||
// file COPYING or http://www.opensource.org/licenses/mit-license.php. | |||||
#include <crypto/common.h> | |||||
#include <cassert> | |||||
#include <vector> | |||||
namespace { | |||||
uint32_t DecodeBits(std::vector<bool>::const_iterator &bitpos, uint8_t minval, | |||||
const std::vector<uint8_t> &bit_sizes) { | |||||
uint32_t val = minval; | |||||
bool bit; | |||||
for (std::vector<uint8_t>::const_iterator bit_sizes_it = bit_sizes.begin(); | |||||
bit_sizes_it != bit_sizes.end(); ++bit_sizes_it) { | |||||
if (bit_sizes_it + 1 != bit_sizes.end()) { | |||||
bit = *bitpos; | |||||
bitpos++; | |||||
} else { | |||||
bit = 0; | |||||
} | |||||
if (bit) { | |||||
val += (1 << *bit_sizes_it); | |||||
} else { | |||||
for (int b = 0; b < *bit_sizes_it; b++) { | |||||
bit = *bitpos; | |||||
bitpos++; | |||||
val += bit << (*bit_sizes_it - 1 - b); | |||||
} | |||||
return val; | |||||
} | |||||
} | |||||
return -1; | |||||
} | |||||
const std::vector<uint8_t> TYPE_BIT_SIZES{0, 0, 1}; | |||||
uint32_t DecodeType(std::vector<bool>::const_iterator &bitpos) { | |||||
return DecodeBits(bitpos, 0, TYPE_BIT_SIZES); | |||||
} | |||||
const std::vector<uint8_t> ASN_BIT_SIZES{15, 16, 17, 18, 19, | |||||
20, 21, 22, 23, 24}; | |||||
uint32_t DecodeASN(std::vector<bool>::const_iterator &bitpos) { | |||||
return DecodeBits(bitpos, 1, ASN_BIT_SIZES); | |||||
} | |||||
const std::vector<uint8_t> MATCH_BIT_SIZES{1, 2, 3, 4, 5, 6, 7, 8}; | |||||
uint32_t DecodeMatch(std::vector<bool>::const_iterator &bitpos) { | |||||
return DecodeBits(bitpos, 2, MATCH_BIT_SIZES); | |||||
} | |||||
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}; | |||||
uint32_t DecodeJump(std::vector<bool>::const_iterator &bitpos) { | |||||
return DecodeBits(bitpos, 17, JUMP_BIT_SIZES); | |||||
} | |||||
} // namespace | |||||
uint32_t Interpret(const std::vector<bool> &asmap, | |||||
const std::vector<bool> &ip) { | |||||
std::vector<bool>::const_iterator pos = asmap.begin(); | |||||
uint8_t bits = ip.size(); | |||||
uint8_t default_asn = 0; | |||||
uint32_t opcode, jump, match, matchlen; | |||||
while (1) { | |||||
assert(pos != asmap.end()); | |||||
opcode = DecodeType(pos); | |||||
if (opcode == 0) { | |||||
return DecodeASN(pos); | |||||
} else if (opcode == 1) { | |||||
jump = DecodeJump(pos); | |||||
if (ip[ip.size() - bits]) { | |||||
pos += jump; | |||||
} | |||||
bits--; | |||||
} else if (opcode == 2) { | |||||
match = DecodeMatch(pos); | |||||
matchlen = CountBits(match) - 1; | |||||
for (uint32_t bit = 0; bit < matchlen; bit++) { | |||||
if ((ip[ip.size() - bits]) != | |||||
((match >> (matchlen - 1 - bit)) & 1)) { | |||||
return default_asn; | |||||
} | |||||
bits--; | |||||
} | |||||
} else if (opcode == 3) { | |||||
default_asn = DecodeASN(pos); | |||||
} else { | |||||
assert(0); | |||||
} | |||||
} | |||||
} |