When working with binary data in C++, the std::bitset container provides a convenient way to manipulate and perform operations on sequences of bits. Sometimes, you may need to find all occurrences of a specific bit pattern within a bitset. In this blog post, we will explore how to accomplish this task efficiently.

Before we begin, let’s assume that you have some experience working with std::bitset and understand its basic concepts. If not, it would be helpful to go through the documentation or any tutorial on std::bitset before diving into this topic.

The Problem

Given a std::bitset of a certain size and a target bit pattern, the goal is to identify all the positions at which the target pattern occurs within the bitset.

Solution Approach

To solve this problem, we can iterate over the bitset bit by bit and compare each possible subsequence with the target pattern. If a match is found, we can store the index where the match begins.

Example Code

Here’s an example code snippet that demonstrates how to find all occurrences of a specific bit pattern in a std::bitset:

#include <iostream>
#include <bitset>
#include <vector>

std::vector<size_t> findPatternOccurrences(const std::bitset<32>& bitset, const std::bitset<32>& pattern) {
    std::vector<size_t> occurrences;
    size_t patternSize = pattern.size();
    size_t bitsetSize = bitset.size();

    for (size_t i = 0; i <= bitsetSize - patternSize; ++i) {
        if ((bitset >> i) == pattern) {
            occurrences.push_back(i);
        }
    }

    return occurrences;
}

int main() {
    std::bitset<32> bitset(0b11010011010100110101001101010011);
    std::bitset<32> pattern(0b101);

    std::vector<size_t> result = findPatternOccurrences(bitset, pattern);

    if (result.empty()) {
        std::cout << "No occurrences found." << std::endl;
    } else {
        std::cout << "Occurrences found at the following positions: ";
        for (size_t position : result) {
            std::cout << position << " ";
        }
        std::cout << std::endl;
    }

    return 0;
}

In this example, we define a function findPatternOccurrences that takes in a bitset and a pattern as parameters. We iterate over the bitset using a sliding window of the same size as the pattern. If the window matches the pattern, we store the starting position in the occurrences vector. Finally, we print the positions where the pattern occurred.

Conclusion

By iterating over a bitset and comparing subsequences with a target pattern, we can efficiently find all occurrences of the pattern within the bitset. The provided example code demonstrates how to implement this solution in C++.