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Fix unaligned memory access UB in compact_vector::access() #11

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Merged
jermp merged 3 commits into from
Oct 6, 2025
Merged

Fix unaligned memory access UB in compact_vector::access() #11

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e5474a5
Fix unaligned memory access UB in compact_vector::access()
adamant-pwn Oct 5, 2025
e16cea2
fix UB in append_bits
adamant-pwn Oct 5, 2025
74fb693
Fix assert
adamant-pwn Oct 6, 2025
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1 change: 1 addition & 0 deletions include/bit_vector.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,7 @@ struct bit_vector //

void append_bits(uint64_t bits, uint64_t len) {
// check there are no spurious bits
assert(len <= 64);
assert(len == 64 || (bits >> len) == 0);
if (!len) return;
uint64_t pos_in_word = m_num_bits & 63;
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5 changes: 4 additions & 1 deletion include/compact_vector.hpp
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Expand Up @@ -2,6 +2,7 @@

#include <vector>
#include <cmath>
#include <cstring>
#include <iterator>

#include "essentials.hpp"
Expand Down Expand Up @@ -253,7 +254,9 @@ struct compact_vector //
assert(i < size());
uint64_t pos = i * m_width;
const char* ptr = reinterpret_cast<const char*>(m_data.data());
return (*(reinterpret_cast<uint64_t const*>(ptr + (pos >> 3))) >> (pos & 7)) & m_mask;
uint64_t word;
std::memcpy(&word, ptr + (pos >> 3), sizeof(uint64_t));
return (word >> (pos & 7)) & m_mask;
}

uint64_t back() const { return operator[](size() - 1); }
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