This example demonstrates the usage of SIMD in JavaScript through WebAssembly. It runs 100000 times the addition of 2 arrays of size 10000 (see index.js for more details).
The first implementation is done with a simple loop in JavaScript:
for (let j = 0; j < arraySize; j++) {
result[j] = a[j] + b[j]
}The second implementation relies on WebAssembly code written by hand in text format. Here is the SIMD specific part (you can find the entire code in simd.wat):
(v128.store
(i32.add (local.get $result) (local.get $i))
(i8x16.add
(v128.load (local.get $i)) ;; a
(v128.load (i32.add (local.get $arraySize) (local.get $i))) ;; b
)
)Here are the execution times I get on my computer, along with few values from the arrays for debugging purpose:
a: Uint8Array(4) [ 103, 64, 32, 55 ]
b: Uint8Array(4) [ 48, 27, 121, 108 ]
--- Simple loop (JS) ---
1587ms - result: Uint8Array(4) [ 151, 91, 153, 163 ]
--- SIMD (WASM) ---
73ms - result: Uint8Array(4) [ 151, 91, 153, 163 ]
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