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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 <vector>
#include <assert.h>
#include <crypto/common.h>
namespace {
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)
{
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()) {
if (bitpos == endpos) break;
bit = *bitpos;
bitpos++;
} else {
bit = 0;
}
if (bit) {
val += (1 << *bit_sizes_it);
} else {
for (int b = 0; b < *bit_sizes_it; b++) {
if (bitpos == endpos) break;
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, const std::vector<bool>::const_iterator& endpos)
{
return DecodeBits(bitpos, endpos, 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, const std::vector<bool>::const_iterator& endpos)
{
return DecodeBits(bitpos, endpos, 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, const std::vector<bool>::const_iterator& endpos)
{
return DecodeBits(bitpos, endpos, 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, const std::vector<bool>::const_iterator& endpos)
{
return DecodeBits(bitpos, endpos, 17, JUMP_BIT_SIZES);
}
}
uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip)
{
std::vector<bool>::const_iterator pos = asmap.begin();
const std::vector<bool>::const_iterator endpos = asmap.end();
uint8_t bits = ip.size();
uint32_t default_asn = 0;
uint32_t opcode, jump, match, matchlen;
while (pos != endpos) {
opcode = DecodeType(pos, endpos);
if (opcode == 0) {
return DecodeASN(pos, endpos);
} else if (opcode == 1) {
jump = DecodeJump(pos, endpos);
if (bits == 0) break;
if (ip[ip.size() - bits]) {
if (jump >= endpos - pos) break;
pos += jump;
}
bits--;
} else if (opcode == 2) {
match = DecodeMatch(pos, endpos);
matchlen = CountBits(match) - 1;
for (uint32_t bit = 0; bit < matchlen; bit++) {
if (bits == 0) break;
if ((ip[ip.size() - bits]) != ((match >> (matchlen - 1 - bit)) & 1)) {
return default_asn;
}
bits--;
}
} else if (opcode == 3) {
default_asn = DecodeASN(pos, endpos);
} else {
break;
}
}
return 0; // 0 is not a valid ASN
}
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