std::find

Use case

Find a specific value in a sequence.

Explanation

Returns iterator to first element equal to value or end() if not found. Must check every element in worst case (element not present or at end).

Time complexity: O(n). Scans elements one by one until found or end reached. See possible implementation.

Code

#include <algorithm>
#include <cstdint>
#include <print>
#include <vector>

// $ echo "nop" | llvm-mc -triple=aarch64 -show-encoding
//	nop                                     // encoding: [0x1f,0x20,0x03,0xd5]
constexpr uint32_t ARM64_NOP = 0xd503201f;

int main() {
  std::vector<uint32_t> instructions = {
      // $ echo "bl 0x40" | llvm-mc -triple=aarch64 -show-encoding
      // bl	#64                             // encoding: [0x10,0x00,0x00,0x94]
      0x94000010,
      // $ echo "sub sp, sp, 0x20" | llvm-mc -triple=aarch64 -show-encoding
      // sub	sp, sp, #32                     // encoding: [0xff,0x83,0x00,0xd1]
      0xd10083ff,
      // $ echo "nop" | llvm-mc -triple=aarch64 -show-encoding
      //	nop                                     // encoding: [0x1f,0x20,0x03,0xd5]
      0xd503201f};

  auto it = std::find(instructions.begin(), instructions.end(), ARM64_NOP);

  if (it != instructions.end()) {
    auto index = std::distance(instructions.begin(), it);
    std::println("Found NOP at index: {}", index);
  } else {
    std::println("No NOP found.");
  }

  return 0;
}

View on GitHub.

Output

$ ./src/algorithms/build/std-find
Found NOP at index: 2