What inherited code has impressed or inspired you?

Question

I've heard a ton of complaining over the years about inherited projects that us developers have to work with. The WTF site has tons of examples of code that make me actually mutter under my breath "WTF?"

But have any of you actually been presented with code that made you go, "Holy crap this was well thought out!" or "Wow, I never thought of that!"

What inherited code have you had to work with that made you smile and why?

Answer 1

Long ago, I was responsible for the Turbo C/C++ run-time library. Tanj Bennett wrote the original 80x87 floating point emulator in 16-bit assembler. I hadn't looked closely at Tanj's code since it worked well and didn't require attention. But we were making the move to 32-bits and the task fell to me to stretch the emulator.

If programming could ever be said to have something in common with art this was it.

Tanj's core math functions managed to keep an 80-bit floating point temporary result in five 16-bit registers without having to save and restore them from memory. X86 assembly programmers will understand just what an accomplishment this was. Register space was scarce and keeping five registers as your temp while simultaneously doing complex math was a beautiful site to behold.

If it was only a matter of clever coding that would have been enough to qualify it as art but it was more than that. Tanj had carefully picked the underlying math algorithms that would be most suitable for keeping the temp in registers. The result was a blazing-fast floating point emulator which was an important selling point for many of our customers.

By the time the 386 came along most people who cared about floating-point performance weren't using an emulator but we had to support Intel's 386SX so the emulator needed an overhaul. I rewrote the instruction-decode logic and exception handling but left the core math functions completely untouched.

Answer 2

In my first job, I was amazed to discover a "safe ID" class in the codebase (c++), which was wrapping numerical IDs in a class templated with an empty tag class, that ensured that the compiler would complain if you tried for example to compare or assign a UserId into an OrderId.

Not only did I made sure that I had an equivalent Id class in all subsequent codebases I would be using, but it actually opened my eyes on what the compiler could do to guarantee correctness and help writing stronger code.