Count Set Bits in an Integer Array

Implement a low-level function such as `uint64_t count_bits(int* arr, uint64_t size)` that returns the total number of set bits across an integer array. Requirements Implement a function shaped like: uint64_t count_bits(int* arr, uint64_t size); Return the total number of set bits across the size integers in arr. Clarify: Whether int should be interpreted as signed two's-complement bits or cast to an unsigned type. Whether the platform width is fixed at 32 bits per int. Whether null pointer with size zero is allowed. Notes The clean answer uses the compiler intrinsic when available: std::popcount in C++20 for unsigned integers, or compiler builtins such as __builtin_popcount. A portable fallback is Kernighan's loop: while (x) { x &= x - 1; ++count; } For performance discussion, mention vectorization and processing wider machine words when the input representation allows it. Do not ignore signedness: cast each element to a fixed unsigned type before counting if the prompt cares about raw bit patterns. Preparation Write both intrinsic and fallback versions in C++. Test zero, all ones, negative values if signed input is allowed, and a large array. Practice the one-line proof for x &= x - 1: it clears the lowest set bit.