Building Your Own Efficient uint128 in C++
Summary
The article provides a practical guide to implementing a fixed-width 128-bit unsigned integer in C++ using two 64-bit limbs, with explicit carry/borrow arithmetic and intrinsic-based multiplication. It demonstrates that hand-rolled u128 can achieve codegen parity with __uint128_t and discusses platform-specific intrinsics, compiler suggestions, and scalability to wider widths.