The linked page has benchmarks - I'd have to go dig into godbolt to see why it's faster. The standard library can actually auto-parallelize, but you have to opt

The linked page has benchmarks - I'd have to go dig into godbolt to see why it's faster. The standard library can actually auto-parallelize, but you have to opt in (see the ExecutionPolicy argument). Edit: I don't know how to dig into the actual implementation of std::reduce on godbolt - it's not inlined. I think the sibling comment has it right though - one can do adds of four at a time with whatever SIMD extensions are available.