WASM array fill performance

array.wat

;; test passing array to and back
(module
  (import "js" "mem" (memory 1))
  (import "console" "log" (func $log (param i32 f32)))

  (global $blockSize (import "js" "blockSize") (mut i32))
  (global $len (mut i32) (i32.const 0))
  ;; len = blockSize * 4
  (func (global.set $len (i32.mul (global.get $blockSize) (i32.const 4))))
  (start 1)

  ;; gain processing function
  (func $amp (export "amp") (param $amp f32)
    (local $i i32)
    (local $x f32)

    (loop $gain
      ;; x = input[i]
      (local.set $x (f32.load (local.get $i)))

      ;; console.log(i, x)
      ;; (call $log (local.get $i) (local.get $x))

      ;; x = x * amp
      (local.set $x (f32.mul (local.get $x) (local.get $amp)))

      ;; input[i] = x * amp
      (f32.store (local.get $i) (local.get $x))

      ;; i++
      (local.set $i (i32.add (local.get $i) (i32.const 4)))

      ;; if (i < len) repeat
      (br_if $gain (i32.lt_s (local.get $i) (global.get $len)))
    )
  )
)

run.js

 const BLOCK = 1024
  var buf = fs.readFileSync('./array.wasm')
  const mod = new WebAssembly.Module(buf)
  const mem = new WebAssembly.Memory({ initial:1 })
  const blockSize = new WebAssembly.Global({value: 'i32', mutable: true}, BLOCK)
  // blockSize.value
  const f32mem = new Float32Array(mem.buffer)
  const importObj = {js: {mem, blockSize}, console:{log(a,b){console.log(a,b)}}}
  const instance = new WebAssembly.Instance(mod, importObj)
  const {amp} = instance.exports
  
  
  let src = Array.from({length:BLOCK}, (a,i)=>i)

  
  f32mem.set(src)
  console.time('wasm amp')
  for (let i = 0; i < MAX; i++) amp(.5)
  console.timeEnd('wasm amp')


  console.time('js amp')
  for (let i = 0; i < MAX; i++) for (let j = 0; j < src.length; j++) src[j]*=.5
  console.timeEnd('js amp')