[nheer]

Author here. There are actually 3 Swift versions in the benchmark:

  - Swift (standard): 893ms
  - Swift (relaxed): 903ms (uses fast-math equivalent)
  - Swift (SIMD): 509ms (explicit SIMD4)

The standard version uses x *= -1.0 which creates a loop-carried dependency that blocks auto-vectorization - same issue as Crystal, Odin, Ada. The SIMD version uses the branchless i & 0x1 trick and is ~1.75x faster.

Fair point that someone versed in Swift would probably use the better pattern in the standard version too. PRs welcome to improve it! The goal was idiomatic-ish code, but I'm not an expert in all 40+ languages.