Building Your Own Efficient uint128 in C++
Summary
A practical, code-forward guide to implementing a fixed-width 128-bit unsigned integer in C++ using two 64-bit limbs. It demonstrates addition, subtraction, multiplication, equality, and comparison with explicit carry/borrow handling and intrinsics, aiming for compiler-generated code indistinguishable from built-in __uint128_t. The article also covers cross-platform considerations (Clang/GCC, MSVC, and AArch64) and notes on performance benefits of fixed-width arithmetic.