At least on x86 processors, most idiomatic bit manipulation expressions like `word & -word` or `word & (word - 1)` compile to a single fast ALU instruction. __b

At least on x86 processors, most idiomatic bit manipulation expressions like `word & -word` or `word & (word - 1)` compile to a single fast ALU instruction. __builtin_clz and similar are comparatively more expensive on many architectures.