not: Wasm SIMD bitwise instruction

Try it

(module
  (import "console" "log" (func $log (param i32)))
  (func $main
    v128.const i16x8 10 23 56 15 25 29 92 45
    v128.not

    i8x16.extract_lane_u 15
    call $log ;; log the result
  )
  (start $main)
)

WebAssembly.instantiateStreaming(fetch("{%wasm-url%}"), { console });

In the above example, the i16x8 10 23 56 15 25 29 92 45 value is stored as a series of 16 hex values in the v128:

Byte index     0  1  2  3  4  5  6  7  8  9  10 11 12 13 14 15
Hex value      0A 00 17 00 38 00 0F 00 19 00 1D 00 5C 00 2D 00

When running v128.not on the value, each value has a bitwise NOT performed on it, meaning that each byte b becomes 0xFF - b:

Byte index     0  1  2  3  4  5  6  7  8  9  10 11 12 13 14 15
Hex value      0A 00 17 00 38 00 0F 00 19 00 1D 00 5C 00 2D 00
Hex after NOT  F5 FF E8 FF C7 FF F0 FF E6 FF E2 FF A3 FF D2 FF

The resulting output v128 value is a i8x16, therefore i8x16.extract_lane_u 15 outputs the value in the last lane. This is equal to 255 (0xff), which is the bitwise NOT of 00 (0x00).

In other words: